They are, assuming you can make RB3 work with these. Any emulated NAND will be compatible with APP files, this is not the problem. The problem is making RB3 to work with said emulated NAND. The only one known to be relatively successfull is the one I posted in the first page, but nothing prevents you from trying other methods.
sorry, I didn’t notice that you answered.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!