I know of at least one player who NEVER has attended a Team One or Baseball Factory event, and yet was invited to the UA-AA event. He got a "Congratulations, you're an All American!" letter.
However, after he chose not to pay, and therefore not to attend, his name was not listed among the "All Americans." This experience matches with that of another player I have seen discussed on this site, in another thread.
My conclusions are that this event was NOT limited to TO/BBF showcasers, but it WAS limited to those who paid.
There's probably a great business opportunity there, if I could only cash in ....