Harmonix's stance is if other developers, namely Red Octane, was willing to help Harmonix to get the Les Paul working on PS3, it will get fixed. In other words, and no, this isn't made up, they want Red Octane to deliver on Harmonix promises.
There is a genuine feeling of being victims of a deception with this issue and unfortunately, it's a rightful feeling. After all, they've been saying compatable compatable compatable this entire time when it was IGN which broke the news that those claims were in fact false. Now their stance is that they'll be more than willing to let Red Octane fix the issue if they want to.
As for a list of confirmed working third party controllers? None, nada, zip, zilch, zero, bupkis. In other words, the only compatable controllers are those which are not available for sale. Now do you see the problem? I mean, EA wonders why they aren't making as much money on PS3. Between broken ports, horrid ports, and this.... I'm wondering why I bought a game where I call up my friend hoping he's not playing so we can snag his strat.