Well, I was discussing this with MarkMan, and he believes that subsequent PS3 firmware updates since his review have rendered the rumble function of the REAL converter useless. The converter still works, but rumble is out. Major bummer. This was totally unnecessary of Sony.
I don't know if this has been addressed, but the REAL converter does work with Guitar Hero 1. I know this because I have been playing it on my PS3 through the REAL for the past few days. My GH1 guitar always had screwy tilt-action star power, but it worked on the PS3 as well as it ever did on the PS2. (I just use the select button instead.) It works well enough that I can get 97% through Bark at the Moon on expert. I'm not saying that the converter has faults that keep me from completing the song. I've never gotten that far into the song before, so the converter is doing its job well. I don't have any other PS2 Guitar Hero games to test it with, so I don't know first hand if GH2 or 80s has the expected problems.