https://musicbrainz.org/doc/Style/Release_Group ought to provide clear guidance about whether instrumental versions of hip hop (and other?) albums belong in the same release groups as the original vocal versions or in their own release groups.

The "Other situations" section currently makes a weak suggestion that separate release groups should be created:

Be aware that attempting to group these releases can be quite controversial. If in doubt, these releases should probably be in separate release groups.

This isn't enough to prevent messy situations like https://musicbrainz.org/artist/aba64937-3334-4c65-90a1-4e6b9d4d7ada where half of an artist's albums use one form and another half use the other.

Separate release groups:

• https://musicbrainz.org/release-group/a1e6c75a-07cd-4b8d-aff5-9f25d010f7b3
• https://musicbrainz.org/release-group/0a14af90-63c8-4caa-9934-37f1eb0d7fca
• https://musicbrainz.org/release-group/1ca14039-8925-4bec-9fff-f9625dfec0ae
• https://musicbrainz.org/release-group/4364ebfe-367b-4273-8657-5e6ad9d964f3

Same release groups:

• https://musicbrainz.org/release-group/9c879c63-606d-375f-aaf7-3618d94655b5
• https://musicbrainz.org/release-group/769966a4-c76b-4935-a5c0-74147dcb5b79
• https://musicbrainz.org/release-group/fff783b6-8190-477c-b526-2fec492b98f9
• https://musicbrainz.org/release-group/c34d3356-a0f8-4d42-8b37-053629a18cae

Edit note discussions where there's no consensus:

• https://musicbrainz.org/edit/100144696
• https://musicbrainz.org/edit/127988147

Forum thread with some discussion: https://community.metabrainz.org/t/new-release-group-for-instrumental-versions/620583

I don't have a strong feeling either way, but the current lack of clarity makes it extremely difficult to know where to look to determine if an instrumental release is already in MB or not.