WolvoGamer has made a pretty great video tutorial on setting up Hustle Kings Cross Play between a PS3 and Vita.
In his example there are two people in the lobby, but there's room for up to 8 players per lobby.
Check the video out here:
http://www.youtube.com/watch?v=5OP5cj2viNY
If anyone has any problems with setting up Cross Play this should answer your queries
