Stainless steel is an iron product just as regular steel, although it has nickle in it, it is still an iron product, I have never heard of or seen a problem of mixing SS with regular steal, we mount SS control cabinets, disconnects as well as SS conduit to steel strut all the time, what about where using GRS conduit to a SS cabinet? it's done all the time, and I have seen some at work that have been in place for years and I have never seen any corrosion where the two metals make contact.
When I think of dissimilar metals I think of copper to aluminium, tin, iron/steel, brass although brass and copper are the same base metals just like SS and iron/steel, I have never seen a problem mixing copper and brass.
Galvinized iron based metals can have problems when mixed with copper, brass or aluminum but not another iron based metal, steel is just iron with less carbon, wrought iron is just steel with even lower levels of carbon actully none, the major components of stainless steel are: iron, chromium, carbon, nickel, molybdenum and small quantities of other metals, but its base metal is iron, we make it at work.
