Just guessing but probably could get the brass welded but need to re-chrome the rim unless you don't mind the area welded without chrome..

I've been thinking of having some COB hoops re-chromed. I'm sure the platers could do the weld job, correct?

Well, not certain about that but they may. They'd have to grind down the weld nice first with a die grinder and stone/sand it smooth before re-plating. Do not know what they'd charge for that or re-plating for that matter. You might be better off doing that part (welding and grinding) yourself to save on the labor.

Oh yeah, also welding something thin like that will want to warp it very easily too. It'll probably need to be clamped down between metal plates to help hold it in place and to help keep its shape for welding.