the official Dreamcast controller adapted with a Mayflash DC to USB adaptor is recognized by the PS3 plugged into one of the USB ports. Did not know this. . .
Just played some Marvel vs Capcom and Sega Rally demo with it. It actually works fairly well except one real catch that pause/start on the DC controller is recognized as L1 and not "start". That is a real problem for any game that requires the actual start button to be pressed as opposed to allowing start via the "a" button, for example, or if you just want to pause mid-game.
My question was whether the DC controller could be used for any of these upcoming DC digital titles and it looks like under these circumstances it can sort of.
Try playing Jet Grind Radio with a Dual Shock and you'll see why using the actual DC controller is *much* preferable.
Oh well. . . share your own experiments adapting DC controllers to next gen console if you have tried.