Let's be perfectly honest here, any accent he may have will be American.
Seriously, don't let something like an accent dissuade you from choosing southern Germany, if you find that's the best location for you (and let's be honest: BMW, Mercedes, and Porsche are all headquartered in the South).
Besides,
every region in Germany has it's own dialect: even the North. It's not as if northern Germany speaks "pure German" while Bavaria is tainted, not unlike English in the U.S.A.; you can always tell where one is from based on their accent (like Minnesota).
However, it would be best to avoid small towns in both the North and South (although especially the South) as their dialects will differ the greatest from Hochdeutsch.
But if you want to go to Munich, for example, I don't see why it would be a bad idea.