So from what I understand, in this case you can use the subnet ID and broadcast address as valid addresses?
Subnet and broadcast are valid addresses anyway. However, they cannot be used as hosts if that is what you mean by valid addresses. Where the subnet host range 150.0.0.1 - 150.0.1.254 the address 150.0.0.255 is not a broadcast address. The subnet spans 512 contiguous addresses. The first is the subnet and the last is the broadcast. Everything in between is a valid host and there is absolutely no difference between say 150.0.0.1 and 150.0.1.1.
Now if you mean the 128 subnets when it should be 126 subnets, this comes down to whether the routers can handle the use of subnet 0. As Smurf said, typically these days, the first subnet is allowed to be used but any say CCNA question on it would say whether subnet zero is being used or not.
