If an account is frozen versus not existing? I know its a silly question, but I really have no clue...

if you put their name in this link: http://www.subeta.net/users/USERNAME (of course replacing USERNAME with their account name), it will say, "Sorry, this account is frozen; Profile may not be viewed."

So if it comes up a blank page, does that mean the name is available?

I'm 99.9% sure that yes, it's available if it comes up as a blank page.