However, when these files are renamed to a .mov extension they play fine.
Ssssh. Don't tell anybody about that
The idea behind not supporting .mp4 is because we really REALLY think it's a bad idea to VJ with it, and it could make Resolume perform unstable. By not loading obviously poor VJ codec choices like .mp4 we send out that message. That aside, if Quicktime can open it, Resolume should be able to as well. You may need to resort to some trickery like this, but it will work.
Hope that explains our standpoint a bit.