you are only allowed to have 1 main forum running and 1 test forum, but the test forum must be in a testvb dir and .htaccess protected.
Running 2 forums on 1 database is just the same as running 2 forums on 2 databases, as both can be totally different inrespect that both can have different forums, user etc.
At least that's the way I read it, and I could be wrong
But if you was allowed to do that then there would be nothing stopping you having 2, 3, 4 or as many as you like and just point a new domain name to each.