So, what's the difference between the RODI waste water and tap water? You should be dosing your macro and micro ferts with planted tanks (Kno3, Po4, etc.) (See:
http://www.aquaticplantcentral.com/f...ing-guide.html) anyways, regardless of method.
Whats the TDS out of the tap? What's the TDS out of the rodi waste water?
I wouldn't see it as a problem. I had high tech planted tanks for years, and I would do it if I had both. It's still filtered through your carbon and sediment filters, so it would be much better than straight tap water, as tap water still has chloramine/chlorine in it for the most part.
I would make a batch of water from the waste water, use your prime with it, then dose your KN03, KH2P04, and trace elements in it before your water change.
However; I would do a test beforehand. I've had fish in waste water before (feeder goldfish) with no problem, so it doesn't strip needed elements from water.
Best of luck!