No doubt. 400W Radium is one of the gold standards in lighting in the hobby, especially for SPS. Most people use HPS ballasts to drive them, or just regular 400W metal halide ballasts and they get great results. I did, especially on lumenarc reflectors. I never drove them with 400W HQI ballasts, so I don't know how that works, but I imagine that it is really good. Pay attention to how many hardcore long-term SPS guys who use the radiums have move on to LED - none that I know of, although a few went and came back, or experimented and were disappointed (like I was). Tons of the really respected farmers, fraggers and other high end hobbyists are firing 400W Radiums right now. They are a great choice.
Here are my top-3 gold standards for SPS/Clam tanks and all of these are not separated by much, IMO:
1) XM 10K 400W Halides and 4x VHO URI Super Actinics - color and par beyond compare, but the VHO require a hood (heat) and these will suck up the power.
2) 250W HQI 14K Phoenix - no hood, no need for actinic anything, low power
3) 400W Mogul Radium - no hood, no need for actinic anything, medium power
I can run #2 or #3 without a hood and without a chiller, so the 10K and VHO option is out for me although the color was probably the best... nothing beats VHO Super Actincs for looks... there is something about that 1.5" bulb that cannot be duplicated with T5 or LED blue.
Somewhere down about #10 would be ATI 8 bulb, or the like with the high quality ballasts and reflectors, with an appropriate combo of bulbs. LED is nowhere on my list.
This is where this will get controversial for some, and many will disagree. I am not a professional photon or radiation expert, nor did I sleep in a Holiday Inn Express last night, so these are my thoughts alone and I don't really care to have an argument. Supplementing LED with MH will only work if you are assuming that the LED are missing spectrum. If you think that the concentration of wave lengths are too much over too small of an area and that this is not optimal for coral, then MH won't help since the narrow, concentrated spectrum will still exist. If the LEDs are giving off harmful radiation, the supplementing with MH won't help, since the radiation will still exist. You can search all over the web and see that a few blue LEDs give off "an insignificant amount" of UV radiation to humans, although this is not qualified or quantified, but there has to be some radiation to have an insignificant amount. These web sites also state that the white diodes that they tested/developed are just really blue diodes with a different film over them to make them look right, so they assume that they are the same. However, I have not seen any test/studies (independent), or even mention of the possibility, that show the impacts putting several hundred of diodes over a super small area with concentrated lenses to inhabitants that rely on light a lot more than humans. What do I think is happening? First, some history. The first metal halide (mogul and HQI) put off terrible amounts of UV and other radiation that was, at first, though of as "too much light" when the organisms were suffering. This was as sucker's argument because the sun was capable of delivering 3-10x as much light and the same things thrived, but this sucker's argument delayed any real improvements. Eventually, the bulbs were tuned and filters made (the glass around the mogul bulbs and the UV glass under the HQI) that made the bulbs really good. This took time and much effort. The same iterations happened with fluorescent bulbs even before. So, back to my thoughts, keeping this parallel from every previous aquarium lighting development in mind... I think that today's LEDs are putting off some amount of harmful radiation that is not bad enough (like the halides) to kill most things, but harmful enough to bleach, kill some and harm corals. Those organisms that can adapt, do adapt over many months and can even thrive. Those that don't die or always look bad and struggle to ever be the same. Does this experience sound familiar? The "too much light" argument is horrible. The sun puts off like 1300 par 12" under the water at my house in Missouri and polyps and SPS thrived outside all summer. I can put 6 250W HQI over my 120G and get like 850 par at 8" deep (where my first corals are) and over 500 in the sand - everything thrives. I think that LEDs are putting out something else, possibly excessive UV or other types of radiation that is not photon based, that harms coral. Is this so hard to believe? Every other artificial light source went though the same iterations for specialized use (aquarium) after development for humans. If this is indeed right, then adding MH will not help too much. These unfounded, unscientific observations are the basis for why I think that you will still struggle to execute the way that you want even if you add some MH to your tank, although it might help.