If you get an appropriately sized RHP, it can raise ambient temps on the cool side as well as create a hot spot. (For example, my 4x2x1 pvc enclosure had a 12 by 15 inch radiant heat panel, and easily raised ambient temps on cool side to 77, hot spot to 93, and warm side to 83~, and my snake room is 68-70 in the winter time) With taller enclosures such as the viv the OP is talking about, I believe that using a UTH for a hot spot would be easier to control, and using either a bulb or a RHP to control ambients would work well.
Usually a RHP would be mounted one one side, but I've seen some people mount it right in the middle of the roof, and probably use it to control ambient temps.
If RHPS and Vivs were financially viable, I would get them for all my snakesEspecially because they look so nice and give your snakes a "natural" living environment. Unfortunately for those of us who want to breed, this isn't economically viable.