All biological filtation will produce nitrate whether you use live
rock, a fluidized bed filter, wet dry or any other biological
filtration technique. The Nitrogen cycle in the aquarium begins with
ammonia which is broken down by nitrifying bacteria (nitrosomonas)
producing nitrite. The nitrite is then going to be broken down by
another nitrifying bacteria (nitrobacters) which break down the
nitrite into nitrate.

The only ways that I know of that remove nitrite from the aquarium is

1. Water changes
2. Plants, Plant break down the nitrate into oxygen and nitrogen
which is then released back into the air
3. Denitrification resins.

I still recommend a fluildized bed filter even if it can't remove
nitrate (but neither can live rock) because it's a very effective and
cheap type of filtration. The best biological filtration method in my
eyes.