Not great diving in Punta Cana. Like Dhboner says, there's a lot of dead reef, though it can still be a fun dive with a decent amount of fish. If your customer wants, he could book a trip to Bayahibe (which from PC, takes a couple of hours by vehicle), where the diving there is much much better.
Check which dive shop operates out of his hotel or to his hotel. I used Seapro, which is all right, but it seems like they cater to inexperienced divers. Scubafun operates out of Bayahibe, and I've heard that they're very good.