Probably. They don't play off the shelf clubs, so it wouldn't surprise me if they have custom tweaked balls too. Doesn't matter though. They could buy their balls at a flea market and still outplay us.

Padraig Harrington tells a story of heading into the play off at The Open at Carnoustie and sending his caddy into the pro shop to buy a sleeve of ProV1’s because he’d come close to running out. He said that the balls the pros used then were the same everyday ball available to all of us.

Mostly false. Now that left dash is available to the public, even fewer play a different ball. Some play prior editions (Duffner was one) and there may be some prototypes that also can be development for next generation design.

Wedge grinds and prototype putters are a different case, as well as custom shafts not in the standard catalog.

If it is true it would have to appear on the approved list to be put in play.

JAM has the key answer. They have to be on the USGA conforming list. There were a few like Don O says, example of the Left Dash, and there is a period when next generations are approved and played before release to the general public. Probably more cases where a pro hoards an old model they love until that supply runs out.