I'm assuming a USB hub will work the same on a PS3 as with any other USB-supporting device.
As for backward compatibility, I'm not willing to pay the premium used price for a used PS3 that supports it. I'm of the impression that they're 50,000 to 60,000 yen, but it's been a dog's age since I last priced them. For PS2 games I'd probably just drag my old PS2 downstairs, bust out with a component cable, and use my Logitech Wireless Action controller for that "DUALSHOCK 3 MINUS MOTION" feeling.