Yep. Definitely looks like an XLR connector. If no datasheets for it can be found, you get to open one up and reverse engineer the pinout.
In addition to power there might be some diagnostics like reflected power or temperature.
To test them you need to figure out the pinout and possible keying.
Then a signal generator with enough power to drive the amp, a power meter to measure the output power and likely some attenuators to protect the power meter.
If your employer has an RF lab, go ask the engineers there if they have equipment suitable for testing them.
But don't expect them to know the power pinout or other DC details like that.