I don't own RB3, but was under the impression that since I owned RB1 and RB2, I would be able to use them in Blitz.
The RB1 export seems straightforward enough; pay $5 on the PSN for an export key, put the RB1 disk in, and go to Options -> Export Songs. RB2 does not seem to have an analogous menu option. So I started doing some research about how the RB2 export works. It seems it's different (and definitely more convoluted), in that you have to go to a menu option in Rock Band 3 (not 2!) to get the Rock Band 2 songs, but only after entering a code on the back of the RB2 form into the internet and getting a token back. It seems like it's not pulling the songs off the disk, like the RB1 export.
It's frustrating, since I thought I'd be able to play the RB2 songs in Blitz, but it seems you need to own RB3 as part of that export process, which is crazy. I guess at that point in time, the only thing it made sense to export the RB2 songs to, was RB3. But now that Blitz exists, it fucks that whole process up. Anyone have any information to the contrary?