It is possible that we are referring to the same Maximillian Hemmer even though the middle initial I have is "J." The fact that your Max was born in 1843 would certainly make him the prime age for Civil War service. The kicker is that in the 1890 Census he is listed as having been a Confederate soldier. Not unusual, many Irish and German men served the South. My problem is that I cannot find anyone with a name closely resembling his on any of the Confederate regimental rosters. Of course he might have served in the CS Navy also.
The two Hemmer's I mentioned in my original query were both CW veterans who fought for the Union.
Is there anything in the Hemmer family lore that would suggest that Max was in the South for any reason just prior to the Civil War?