I must admit, that I wanted to express my general doubt about ground isolation and separated grounds in RF and high frequency circuits in the first place. Nevertheless, there may be cases where isolation of circuit parts is reasonable. But I didn't hear an indication, that it would be with your design.
The original question is about isolation of a RF connector's ground. Why? The coaxial cable shouldn't be expected to carry common mode currents. If it does though, common mode chokes would be the appropriate means. The more interesting point is about the signal current sourced from the connector, it's forward and respective return path in the circuit. If it's not designed properly, interfering currents may be injected into the common ground plane and possibly emerge at other places. At least, it can be a source of radiated interferences. In case of logic signals, differential signalling is the ultimative means to get rid of this kind of problems.