I have been playing with my cousin in the Toy Box Mode for over a half hour and the game works. Massive glitches though such as not being able to see them walk, drive or ride any mounts for a bit. Obviously this needs to be fixed with future patches, but it does work. Note, headsets do not work and based off the box, voice chat is not included in the game. Please someone prove me wrong, but for now we are using Skype to talk while playing.
I did shut down my system and restart the game to see if the corrupt saved data message would come up and it didn't.
WORD OF WARNING! A patch was not released, so your travels may vary so attempt at your own risk.
Five people are confirmed playing without any issue that I know of. Three members (me included in the three) on here which can vouch that this works. Good luck!