To address your first question: The answer is THEIR answer, and it will solely their choice whether or not to include humor (or attempts thereof).
To address your second question: That's entirely your call, I don't think this needs to be a hard and fast rule. To blanket down-mod "funny" (now you have to quantify 'funny') seems a touch ridiculous.
Some have argued that "it goes against what the site is about", but that's just it, it's moderated by the community. Not any one or two or three opinions.
Perhaps I'm of the mindset that I won't mod up unless it is funny. Maybe I read a really,really misguided answer and think that its "funny" in a different way....
I think the point of user\community moderation is that you moderate what your gut tells you instead of following some pre-described rules or consensus verbatim.
Rectum? it nearly killed 'em! Bamp-rump-bum!