So I tested my GPWiz40 Roto, and it worked fine. I configured it in EmulationStation, and was off to the races.
As far as the roto-x support, there's no software (that I'm aware of) to adjust the speed of the Roto-X stuff on linux or do anything that the windows software does, but I think you should be able to adjust sensitivity in Mame. I haven't tested this part, but the key presses worked as expected, 3 buttons were sent in the correct order when I spun the LS-30 clockwise and counter-clockwise.
I have a panel already set up with the GPWiz & an LS-30. It used to be attached to a machine that used to have Windows (but only has a PI these days). So, I have a testing unit that I can hook up and on the Pi if you need any more info. It only takes a few moments to do so.
If you haven't tried configuring it in emulation station first, then I'd suggest you do that. If that doesn't work, I can tell you how to test in Linux to see if it's even recognized. If you have a PC, and it works on that, then (other than possibly the rotary control) the rest of the encoder should work fine on a Pi.
I have emailed the company twice and they do not respond.
I get this on and off with them on questions that can't be answered easily. Usually they eventually get back to me, but occasionally it takes a long while. If you get desperate, Randy posts on this board from time to time. You could try PMing him if I can't help you further.