It's been a while since I had my G-System, so I don't remember what the protocol for that unit is.
However, if the VH4 is set to OMNI, it shouldn't matter what channel the G-System uses.
Sigma is right, the VH4 and Diezel's in general use PC mode for midi communication.
You can set the channels, use the inserts, etc. however it is all on one program change. You can't turn them on/off individually.
The G-System may be using CC mode because it can turn effects on/off. Yet, it should be capable of both.
You may wanna ask TC Electronics or head over to a TC forum and ask that question, just to check it out.
Sorry I can't be more help...Good Luck