I just want to point out --- Allmusic is a dreadful site. Full of errors, duplicates, and omissions.
But also, "non-featured" performers means different things to different people.
Depending on what you specifically mean, a site like Allmusic doesn't list non-featured performers, or, again, depending on what you mean, it is a list of the non-featured performers.
I only bring this up because one of the music unions has a list of unclaimed royalties by "non-featured performers" due to a change in some copyright laws. They are typically studio employees/musicians who get a weekly salary regardless of if they record with someone or not, and really are only recording on a particular song because it was (as example) Tuesday at 2pm, which was their assigned time to be available each week. And therefore were previously not entitled to a credit or a royalty - especially when the next day, it was someone else doing the same job. And you may not know who's actual "track" was the one that was used.
You'll find many previously "nameless" people being credited with performances because of the law change.