Collin,
You shouldn't have to do anything. The 3550s will pass the traffic, no matter what the TCP or UDP port is. All you need to do is not have an access list that blocks UDP 427 on any applicable interfaces. Clients will connect to the server(s) on this port, and the switches will simply pass the traffic.
To verify that UDP is good accross a WAN, verify that the clients can ping the server. Then have the client attempt to reach the server for the specified service. If the ping is successful but the client-server application fails, the only way that the switches can be at fault is if, again, there is an access list on the path that blocks the UDP port.
HTH
Mark