Yep. Basically just that if you are on 360.
Most ekits output their MIDI in a way that works perfect with that adapter. The only one that might be an issue is if you have a hi-hat pedal. Mine corresponded to a kick drum, while some will actually trigger an open/closed hi-hat. You may have to tweak the midi notes yourself on the brain to fit if there are any issues.
In my opinion it's best to leave the hi-hat pedal alone while playing Rock Band. However, you can tweak the midi notes to whatever buttons you want (with the exception of control sticks, directional buttons, select, and start) so if you want to try using your hi-hat pedal for a second bass pedal or whatever else, you can. I have my hi-hat pedal to activate yellow cymbals, haven't really gotten much use since I already have two kick pedals though.