[There was a bit of a similar discussion on Highlights releases: same or different RG?]
I kinda feel like these should be their own RGs, linked to the album but hidden by default since they contain only promotional releases. I don’t feel like you can really claim a 5 track sample is at all equivalent to the album itself. In the end though, it probably doesn’t matter much since @IvanDobsky probably has a point that the people who care enough to collect a sampler are also the people who won’t care much about “having this album” but about having specific releases.