I'm not sure which Adzen model it was but it suffered greatly from crosstalk. (This was about 6 years ago so maybe they've fixed that problem)
However, 2 transmitters/2 receivers on different frequencies should be fine whether it's UHF or VHF.
If your camera mic is detachable you could do the boom pole thing--tape it to a broom stick and have it wired in and held OVER THEIR HEADS out of picture. Or you could do it anyway and record the audio to tracks 3 &/or 4 if your camera can do that. (or 1 &/or 2).
I do this alot wired directly in to the camera.