Same belief here, it should work.
I assume your going to make 7 pins on each side of the long cable and then short harnesses going to the Wendt and camera respectively.
First of course, how you connect things in the connector is only part of the story. The next part is the cable. It of course depends a bit on how long you make the cable. Balanced signals can run quite a long way, 300 feet is not unheard. But the unbalanced return signal will be a bit more susceptible to interference. I would believe you could run maybe 100 fett without too much trouble, my guess only.
You could definitely run this in a 6pair cable with single shield. Some are to be found, again some of them are a bit on the bulky side. Soldering 7 pins in the cable is crowded, takes a bit of experience. Running the unshielded return next to the mic level signals may get you a bit of interference between the two, but again, my guess is that it would work.
Next again is the possibility of ground loops in the harness going from the 7pin to the Wendt. If you get into troubles here, you could diminish it by connecting the pin 1 ground only to the RTN ground, not to the 3-pin XLR-s. The output signal as such only goes on the hot/cold cables, the ground is there to make sure that there is not too much of different ground reference for the two units. The RTN signal, beeing unbalanced, of course referrs to ground. I would do this only as a trouble solving effort though. Same kind of discussion goes for the camera side of things.
A final note: 7 pin XLR-s are used here and there for connecting tube microphones to their power supply. This means 200V or a bit more. If accidently connected to the wrong output, you would fry your equipment.
// Gunnar