Hi Eric,
Great questions.
I work with a couple of Radio Dramas, and there are definitely some plusses and minuses.
On the plus side, it will give you some practice reading, using the mike, editing, dropping to mp3, and possibly using FTP. Depending on the role and production, it may give you some chances to test the acting waters. If your time and money are limited, it's an ok way to play around.
On the "not-so-plus" side, it is not the quickest or best route (IMHO) to gain the acting skills you need to excell in this business. Live Theatre and Improv will get you there much faster. Ideally, you'll also need to be playing with people who are above your current level. Don't wanna end up in a blind-leading-the-blind scenario. A good coach or director is a much better option.
On the second question, yes, a lot of these groups operate in the grey area legally. They basically get away with it because they are too small to make a dent. But make no mistake about it: the productions that use copyrighted characters are not on solid footing legally.
As an alternative, there are a number of groups with completely original productions being made all the time. Two that I work with are Wormwood (
www.wormwoodshow.com) and Dream Realm (
www.dregold.net). There's also Pendant Audio - they do a fair number of original productions as well.
Hope this helps a bit,
Joe J Thomas
www.JoeActor.com