A119: Philosophically I wouldn't go that direction for a couple of reasons*, but from a rules standpoint you've basically called it. DM has discretion over what checks can be aided, and there's nothing in the rules that says otherwise with regards to monster knowledge checks.

Spoiler: *
First, because it makes sense to me that at least one other person could help with a comment that jogs the main person's memory, and second because I think the game plays better when the players have more information. But that's just what's most fun for me.