Welcome to AMHD.
I can see why you answered the way you did, but the way the question reads it is clear that Sland4 was talking about a vacuum breaker and NOT a vacuum relief valve...
As an example, they said, "I purchased a vacuum relief valve and the installation instructions that came with it states that it should be installed on a horizontal line above an elbow...(directly above the vertical line that feeds the tank)". This is not the description of a vacuum relief valve... agreed?
Then, in post #3 Sland asks, "Does the breaker
need to be above or below the shutoff on a vertical line?" If it was, indeed a vacuum relief valve, I would have expected Sland to correct me at this point.
I also figured that this job was being reinspected as Sland said, "In order to gain occupancy, an inspector informed me that I need to install a vacuum relief valve on the cold water supply line for my hot water tank."... so if I was off base I figure they would have been back by now to tear my head off!
Finally, I just posted all this to kind of show you what my thoughts were when I answered the question. After a few thousand (or more) posts you kind of learn to read between the lines.. ya know?
Anyway, thank you for posting your thoughts as you saw them. I completely understand and am glad you posted your safety concerns!