Quite common these days. Logica, capgemini, big4 and IBM all use contractors as part of on site teams. Some do this with agencies but many do it direct.The only real issue is are they creditworthy enough to pay you, or will they need to wait for the banking client t pay them before they can afford to pay you? Their payments may well be staged by project phase, but I assume you'll want to invoice monthly nd be paid promptly.