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"That creature" being the creature that triggered the spell. So the space that the spirit would have to be summoned into will be the space of the triggering creature, not an unoccupied space, and so the summons will fail, even if you can store the spell. And this happens to be true for all the conjuration spells that target a space. So strict RAW, successfully casting summoning spells from a glyph, even though it is clearly intended, based on the mechanics of the glyph cannot work. It would be up to your DM to fix this.

So who is the caster in that case? Is it still you? Or is it the glyph? I think it most likely is still you, as the glyph would not be able to make any decisions for a spell it released, like issuing commands to a summoned creature, because it ends on triggering: "Once a glyph is triggered, this spell ends." But this is not explicit, so again up to your DM.

The undead spirit from summon undead is not hostile, so the clause that it will attack "the intruder", that is, the triggering creature, will not apply - thankfully, otherwise it might end up attacking you, because you triggered the glyph.

"That creature" being the creature that triggered the spell. So the space that the spirit would be summoned into is the space of the triggering creature, not an unoccupied space, and so the summons will fail, even if you can store the spell. And this happens to be true for all the conjuration spells that target a space.

So strict RAW, successfully casting summoning spells from a glyph, even though it is clearly intended, based on the mechanics of the glyph cannot work. It would be up to your DM to fix this.

The glyph also says

If the spell summons hostile creatures or creates harmful objects or traps, they appear as close as possible to the intruder and attack it

This would create an alternative if you summoned a creature that is descibed as hostile. Such a creature would instead appear in a space as close as possible to the (triggering) intruder. Unfortunately, none of the conjuration spells in the PHB, states the summoned creatures are generally hostile, and neither does summon undead, so RAW that clause will not apply, and the spell would still need DM fiat to work this way.

So who is the caster in that case? Is it still you? Or is it the glyph? I think it most likely is still you, as the glyph would not be able to make any decisions for a spell it released, like issuing commands to a summoned creature, because it ends on triggering: "Once a glyph is triggered, this spell ends." But this is not explicit, so again up to your DM.

It is a little trickier with portable hole, where you need your DM to agree it is OK to consider the distance to be normal distance through the opening of the open hole. In that case, you can cast the glyph on the wall of the hole - then you do not have to move it, as the wall is in another dimension staying put, and when you open the hole and cast summon undead in range to trigger it, the trigger is in range without ever movign the glyph.

There is the question if you can even store a summon undead into a glyph, because you can only store spells that target a single creature or an area. The targeting rules are unfortunatley rather vague. The normal spellcasting rules do not allow you to even target an area, they only allow you to target

A point of origin for an area of effect is not an area, it is a point. So technically, NO spell in the entire game can fullfill the criterium that they "target an area", and we have to interpret what this means. It could mean that it needs to be a spell that targets a point of origin for an area, or it could be a spell that mentions an area. Both are valid interpretations. Summon undead, similar to other conjuration spells says about the spririt,

"That creature" being the creature that triggerd the spell. So the space that the spirit would have to be summoned into will be the space of the triggering creature, not an unoccupied space, and so the summons will fail, even if you can store the spell. And this happens to be true for all the conjuration spells that target a space. So strict RAW, successfully casting summoning spells from a glyph, even though it is clearly intended, based on the mechanics of the glyph cannot work. It would be up to your DM to fix this.

It is a little trickier with portable hole, where you need your DM to agree it is OK to consider the distance to be normal distance through the opening of the open hole. In that case, you can cast the glyph on the wall of the hole - then you do not have to move it, as the wall is in another dimension staying put, and when you open the hole and cast summon undead in range to trigger it, the trigger is in range without ever moving the glyph.

There is the question if you can even store a summon undead into a glyph, because you can only store spells that target a single creature or an area. The targeting rules are unfortunately rather vague. The normal spellcasting rules do not allow you to even target an area, they only allow you to target

A point of origin for an area of effect is not an area, it is a point. So technically, NO spell in the entire game can fulfill the criterium that they "target an area", and we have to interpret what this means. It could mean that it needs to be a spell that targets a point of origin for an area, or it could be a spell that mentions an area. Both are valid interpretations. Summon undead, similar to other conjuration spells says about the spirit,

"That creature" being the creature that triggered the spell. So the space that the spirit would have to be summoned into will be the space of the triggering creature, not an unoccupied space, and so the summons will fail, even if you can store the spell. And this happens to be true for all the conjuration spells that target a space. So strict RAW, successfully casting summoning spells from a glyph, even though it is clearly intended, based on the mechanics of the glyph cannot work. It would be up to your DM to fix this.

It is a little trickier with portable hole, where you need your DM to agree it is OK to consider the distance to be normal distance through the opening of the open hole. In that case, you can cast the glyph on the wall of the hole - then you do not have to move it, as the wall is in another dimension staying put, and when you open the hole and cast summon undead in range to trigger it, the trigger is in range and the glyph will summon an undead spirit.

It is a little trickier with portable hole, where you need your DM to agree it is OK to consider the distance to be normal distance through the opening of the open hole. In that case, you can cast the glyph on the wall of the hole - then you do not have to move it, as the wall is in another dimension staying put, and when you open the hole and cast summon undead in range to trigger it, the trigger is in range without ever movign the glyph.