no, at least 2 per server(node) to ensure validation is successful. according to the OAC microsoft 70 646 exam book. there is also 5 more requirements for validation, i can tell you those
*nodes must be 2k8 datacenter or enterprise edition
*must have same level service pack installed
*nodes' computer accounts must be in same domain and organizational unit
*must all be member servers or domain controllers, but not a mix of both
*must all have same cpu architecture (32-bit,64-bit, IA64)