PS3News have been successful with running PS3 Retail game back-ups on a PS3 Test from both Internal and USB HDD (along with DVD). Unlike PS2 and PS1 development systems, a PS3 Test won't play a 1:1 copy/scene release.
It only plays development copies, so the executables (EBOOT.BIN) had to be decrypted and rebuilt for them to load. However, as mentioned previously, the executables also had to be patched to eliminate some disc checks.
VERY cool being able to run PS3 Retail Games via HDD though, and now PS3News can tinker with game data to find a potential flaw in how a game handles included files!