Re: if you release music do you have to use your real name?
Nope, liner notes is just liner notes. They don't mean anything legally.
Very likely if the label is paying someone who is using an assumed name they've registered that name with the government as a DBA - Doing Business As. Costs about a hundred bucks at the courthouse and gives you a document that states that checks to Aphex Twin can be cashed by Richard D James.
In fact, I've been told it's good practice for producers to sign contracts as their pseudonym and not their legal name - that way if they want to produce under a different name for a different label, they aren't bound by exclusivity clauses.
EDIT: note that I Am Not A Lawyer.