I just saw this thread otherwise I would have answered earlier. I stayed at the Oriental in August. I don't remember a no shorts/no sandals policy. In fact, the hotel was less formal than I expected, far less formal than the Four Seasons where President Bush stayed.

I wouldn't worry about a dress code. The Oriental is known for its service and you'll have a great time.

As for Singapore, there are a number of great hotles there. I only stayed at the Shangri La and I thought it was fabulous. Its food buffet was by far the best and most extensive I have ever seen. There's also a Raffles Hotel that is highly rated. Tom.