I'll admit, I just voted YES! because Merman has been a long time favorite of mine for MotU.
I felt jipped that he wasn't in the '87 movie.
I'll feel jipped if he's not in this one.
But of course, he should only be there if it makes sense for the story.
Still, even if he's just a background cronnie of Skeletor's that we don't see much of, that'd be okay too.