Cpython has non-moving GC so this is not an issue. On the other hand CPython's hashmap implementation is probably most educational open source hashmap implementation that you can find, because it is full of wonderful and portable performance hacks (for one thing the hash values of CPython's objects is intentionally computed such that the distribution is non-uniform which allows tuning of the hashmap implementation for common cases).

As for having tight coupling between moving GC and hashmap implementation there is another reason why you want to do that: weak pointers and hashmaps that are either weak keyed or weak valued which both are things that are useful for the VM implementation itself (symbol tables, method dispatch caches, identity maps for FFI...).