In case anyone is still wondering about this topic, the answer is no, Rock Band 3 customs are only available on the "crapbox" at the moment.
Custom authors such as myself create custom songs using two programs that they use for the Rock Band Network, Reaper and Magma. Then, we use another user-created program to finish the song.
The RBN was designed for the 360 because Harmonix believed it was more versatile for custom song creation. I don't know the specifics, but I'm guessing that XNA was more compatible with the 360.
But that's beside the point. It could be possible for custom songs to work on PS3 if someone could create a conversion program. After the song goes through Reaper and Magma, someone may be able to create a program as a substitute for the user-created program we use now. I'm pretty sure that the MID file (the notes you play) and the MOGG file (the game audio) would stay the same regardless of the console. All someone would need to do is create a conversion program for all the text files and such.
And, of course, you have to be able to get the final product on your hard drive somehow.
So why is a "crapbox" user such as myself mentioning all of this? Well, quite simply, one of my friends owns a PS3, and he was originally going to author songs alongside me but he stopped when he discovered he couldn't use them on PS3.
Hope this is helpful.
