Have establsihed a lab to test IP DHCP SNOOPING prior to implemntation. So far everything works as advertised. Given that the Uplink port of a switch must be trusted, why is it not necessary to add the trust to a access point?
DHCP snooping works by inspecting DHCP packets and dropping any such packet received on an untrusted port that is of a type sent by a DHCP server (most often OFFER, ACK and NACK).
The reason that you don't need to trust an AP port is that you should only be receiving client types of DHCP traffic on that port. While you receive DISCOVERY, REQUEST and INFO packets, you should not be receiving any OFFER, ACK or NACK packets on the AP port.
The caveat to this is that if you are using the AP as a bridge for a redundant path, then you would need to trust the port. If the primary link were to fail, then you would be passing DHCP server traffic back down to clients through the AP.