It seems clear that there will be a couple of mechanisms in place to keep UGC creators from sharing content that treads on copyrights - using likenesses of established characters, for example. Would it therefore be possible to allow UGC creators to put their own music into their episodes? If the music is terrible, it will weigh heavily on their ratings. If the music is encumbered by copyright, it will be flagged and the content blocked.
Ehh, I'd rather not. No need for some thrash metal band to use STO as a prop for getting an agent.
And that's really the issue here. Once you create an episode, anything in it becomes property of cryptic.
What you say is true, but if the music stinks that's going to trash the rating for that whole episode. You have an incentive to make music that makes sense.
Your second point raises an interesting IP law question I can't answer. As I undertstand it, we're being given assets that have been created by Cryptic for our use, to create content that they are hosting and likely will claim the rights to in total. When and if we have the ability to create our own assets, I imagine those same claims will be made for them. But what of podsafe music I pull in from a web site or a soundtrack I spin out of garage band loops? Does my using those "free" sources of media in a UGC mission make them not free anymore?