I got to weld in piece of steel to replace a pitted piece of stainless. it is not anything structural just cosmetic. if this is possible can i mig it or will the two metals oppose?
No, you can weld it in, without problem, but it will rust up into the stainless a little.
I use to use 6010 arc to weld in stainless fittings, in the oilfield. It kind of defeats the purpose, but it does work.