My two cents, as I don't claim lighting expertise, adding T8 lights will add some par and can add to a successful tank. Many years ago, salt water tanks were kept only using using T8's. Having said that, only using T8's did severely restrict the corals that could be kept. The advances in technology with lights that supply a "better" spectrum and intensity have broadened the species of coral that can be successfully kept. I'd be surprised if you can buy cheap led florescent replica bulbs and keep some of the harder/more demanding corals, with or without adding supplemental T8's. If all your going to keep is mushrooms and zoanthids, you probably can't go wrong, but I'd be surprised if that setup worked with most of the available corals.
I built my own light using led's and T5's, but I researched and bought marine specific color/spectrum leds and ATI T5's for a marine aquarium. (Blue plus and coral plus bulbs.) My setup does work, but I doubt it works better than a purpose built marine light. A friend of mine and I bought a couple of frags of the same coral at the same time and his have grown a lot faster/more in his tank under far more expensive lights than what I have in my tank. It's alive and doing well in my tank, it's just not growing as fast. Of course there is always other factors than lighting too, so it might be a moot point, it's impossible to say.
