I'm not crazy about UGF's, "R" or otherwise. I've never had much luck with them either with or without plants. I did use them once where I had a lot of plants and my stand was open on the bottom and you could see the roots completely filling the UGF space. An interesting idea to me would be to experiment with circulating nutrients (aka hydroponically) in the UGF space but not through the water column (i.e. pumping very slow flow of nutrients down one lift tube and out the other lift tube. This would have an advantage of providing nutrients to root-feeding plants and yet not give algae the access to either ferts or light. Just a crazy dream I had one night, I guess.
One "theory" about UGFs is that they tend to move nutrients past roots too fast for them to be incorporated successfully by some plants. My guess is that many low-light plants tend to be slower growing and consequently not in such demand for either CO2 or fertilizers. But that's just my gut feeling as I don't have a lot of direct experience to quote from.
My UGF tank eventually "plugged" due to roots and detritus, rendering the filter useless. An RUGF is going to put nutrients (that would normally collect in the root zone) back into the water column and from my experience will create algae problems. Regular water changes can mediate this somewhat. I eventually pulled the lift tubes and plugged holes with gravel and went to a dual HOT filter which worked OK. I have cannister filter and 1000gph pump which keeps things pretty clean and still allows minimal substrate "messing" which has always caused me algae problems.
