Can I hang black gas pipe with copper hangers? Is corrosion a concern?
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.
Based on the wiki article galvanic corrosion, I would not use copper with iron pipe:
Statue of Liberty Galvanic corrosion in the Statue of Liberty Regular maintenance checks discovered that the Statue of Liberty suffered from galvanic corrosion
A spectacular example of galvanic corrosion occurred in the Statue of Liberty when regular maintenance checks in the 1980s revealed that corrosion had taken place between the outer copper skin and the wrought iron support structure. Although the problem had been anticipated when the structure was built by Gustave Eiffel to Frédéric Bartholdi's design in the 1880s, the insulation layer of shellac between the two metals had failed over time and resulted in rusting of the iron supports. An extensive renovation was carried out requiring complete disassembly of the statue and replacement of the original insulation with PTFE. The structure was far from unsafe owing to the large number of unaffected connections, but it was regarded as a precautionary measure to preserve a national symbol of the United States.