Not really, Paul. There were plenty of folks of Germanic extraction whose family had been here over a century that were not particularly keen on secession. My g-g grandfather was one of them in Missouri. From what I've learned it appears one of his namesake ancestors (of the generation 1st born in the U.S.) was at Valley Forge in the "German Regiment" of the Continental Army.
There were of course some descendants of German immigrants with Southern sympathies but I wouldn't classify them as "many." "Few" would be a better descriptor from what I can tell although as with any group exceptions will be frequent. For new arrivals, post 1840, the pro-Union effect was likely more pronounced.
At any rate, I don't think Hal intended any offense so I think Don overreacted a bit. I suspect that the comment was more the equivalent of "Black Jones" or "Smith"--but of German ancestry. Could even have been a reference to what were referred to as "Black Republican" politics--the way German immigrants voted during the timeframe of the ACW.
On the flipside, as a lady of Southern extraction mentioned to me in Cooper county last week, she had toured an old cemetery somewhere and asked the keeper why their were no Confederate graves. He responded that was the way it was, and she wouldn't find any Democrats buried there either. (Never mind that the parties have swapped ends since the Civil Rights Act and the Dixiecrats have been slowly replaced by the GOP southern conservatives.)