Are dynamic linkers interchangeable?

I’m assuming that by “dynamic linker”, you’re referring to the dynamic linker/loader, typically known as ld.so, rather than the linker used when building programs, ld.

The dynamic linker/loader is tightly coupled with the C library it is associated with, or even part of. On Linux as typically discussed here, the usual loader is the GNU C library’s loader; if you look at its symbols, you’ll see that it pulls in symbols from the C library:

$ nm -D /lib/ld-linux.so.2 | grep -E ' A|D '
00028898 D _dl_argv
00000000 A GLIBC_2.0
00000000 A GLIBC_2.1
00000000 A GLIBC_2.3
00000000 A GLIBC_2.4
00000000 A GLIBC_PRIVATE
00028f28 D __libc_enable_secure
00028f24 D __libc_stack_end
00029040 D _rtld_global
000288a0 D _rtld_global_ro

See How can the dynamic linker/loader itself be dynamically linked as reported by `file`? for details of how this works.

Alternative C libraries provide their own dynamic loaders; for example, programs built with musl on x86_64 specify their “interpreter” as /lib/ld-musl-x86_64.so.1, which is a link to the musl C library itself:

$ ls -l /lib/ld-musl-x86_64.so.1
lrwxrwxrwx 1 root root 25 Jan 23  2019 /lib/ld-musl-x86_64.so.1 -> x86_64-linux-musl/libc.so

Loaders rely on features provided by their associated C libraries, and vice versa. It would technically be possible to replace a given loader with a compatible implementation, but you’d effectively be rewriting the existing loader, at a minimum. While the basic specification of a dynamic loader is well defined and bounded — loading an ELF binary (on Linux), associated dynamic libraries, and performing the necessary relocation etc. — and one might therefore imagine replacing any given loader with another, the implementation details are all significant.

Note that as long as each dynamic loader has a different canonical name, it is possible for a single system to have different loaders, used by programs as appropriate. This is how it’s possible for a GNU C library-based system to also be used to build and run musl binaries, and opens the way to efforts such as llvm-libc, or even historically, the switch from libc.so.5 to libc.so.6.

They must be interchangeable.

A good discussion about e.g. ld vs gold could be found here: https://stackoverflow.com/questions/3476093/replacing-ld-with-gold-any-experience

Also check this: https://stackoverflow.com/questions/29361801/is-the-lld-linker-a-drop-in-replacement-for-ld-and-gold

There's also LLD from the LLVM project which promises to be the fastest of them all.