Devices you connect to port 30175 must support GpsGate Server protocol. gt30 does not support that protocol. You can ask the manufacturer to implement the protocol and it will work. The protocol is open and the specifications can be found in "GpsGate.com Client SDK" to be downloaded here:
You can also try to connect to "SmartPipe" on port 30176, this port analyzes the data sent and tries to extract time and position information. It works for many devices, but not all.