Is corrosion a concern when hanging black iron pipe with copper hangers?
Galvanic corrosion is a worry only if there is complete circuit.  With water pipes, cold water running through the line can make the wood conductive, so you use copper tape with copper lines.  Gaslines in the house aren't going to be damp.  

If you are worried about it, Insulate it.  Put two turns of duct tape around the pipe whereever you're going to put a hanger.