There is a resemblance there, I'll grant you that. When looking at the picture the first time, I also picked out the same person as the suspected Adolf. But, I don't actually think it's him. For one thing, Hitler had a much more pronounced brow than the man in the photograph. But that might also be the lighting.

Unfortunately, the only way you're ever going to find out with any degree of certainty is to determine what units your great-granduncle served in. Hitler's wartime record is relatively easy to look up, so that's not going to be the hard part. I would suggest going and getting that information - your great-granduncle's war service records - and then come back to us.

Hitler was a member of the 16th Bavarian Reserve "List" Infantry Regiment. If you knew which regiment your family member served in, that would help. Also of interest here is the fact that your family member was a "radio operator/signal man". Hitler was a "runner", and although I don't know the exact organization at the time, runners would probably be grouped with signalers in a HQ element. Hitler would have probably 'hung out' with signallers.