Im new to hydro, but have many years of experience from fish tanks, so take this with a grain of salt.
The uv unit would work very well to keep the water in the res sterile, so its a great way to prevent problems and kill algae (including cyano) etc. in the water.
It will not do anything to any pathogen already established in the root zone (assuming flood and drain), for that you still need some kind of agent in the water.
I think you could easyly get away with running a uv unit instead of the maintenance dose of h2o2, if you keep an eye out for problems and use h2o2 to fix it when they show up.