That doesn't appear to be the case. I just logged on with my friend's account and he could play LBP just fine. How would it know? Unless the download is personalised for user account, there's no way the beta could know who's copy I'm running.
It has to be said, this is the best lit game ever. Even a simple coloured blocks level looks fabulous because of the GI/AO quality illumination. The platforming takes a bit of getting used to as SB really can't jump high onto objects, which is good as it lends more to puzzling. The intro period is a bit long, some 2 hours before you can really paste any objects together, and then zillions of object tutes to do before you can use a tool. So I've only had a cursory glance before being whisked away to Deepbrown's technical extravaganza.
BTW Deep : I looked up typing a message but it was too much trouble! The voice chat appeared to work, unless that other player was psychic or by coincidence his phone was going too! I couldn't see any lipsync on me though. When I first started the game, my Sackboy was talking with Stephen Fry's voice, as the camera was picking up the TV audio and SB sync'd to it!
The important discovery was grabbing works at all heights. As long as there's something to grab nearby, even another player!, SB will grab.