multiple frequencies grounded to same ground bus bar
Absolutely not

Two Rules in NEC intersect to cause this.  

First, different frequencies are by definition and nature different services.  You can't put two services in the same panel (unless the panel is specifically listed for that use). That's because you can only use an electrical part according to its labeling and instructions which are part of its listing and testing at UL etc.  

When a manufacturer submits a device for listing, they include draft labeling and instructions, which they revise if necessary to narrow it down to something UL can test and is willing to list.  "Multiple services" is such an off-the-wall requirement that it is difficult to imagine UL would test panels for that. 

Second, your grounds (Equipment Grounding Conductor) for any given circuit must go back to the same panel the circuit comes out of. Particularly look at the ground-retrofit rules, which allow grounds from the same panel to be mixed promiscuously, but not from different panels.   You can't mix grounds from different panels.. At least not Equipment Grounding Conductors.  These  different services can and often must use the same Grounding Electrode System, but that join will be outside the panels.