Ummm, if they work for DNS they won't drive ground rods. We're not allowed. Not only that, but just driving an 8' ground rod in the ground does not count as a valid ground in most areas (and it's a great way to set up a ground loop). I know around here, and addition ground rods have to be back bonded to the original house ground with #6 copper. If the job can't be properly grounded to an existing NEC approved ground, we don't do it. The customer may reschedule a job and have a qualified electrician install an additional ground rod where required for the install.
The TV2 signal is an Agile modulated output and can be set for any cable channel from 73 - 125 (skipping some channels in the 90s for some reason), so it should be able to be integrated into your cable for your TV2s. I have done this quite often using a simple splitter as a combiner.
The reason I recommend seperate lines, is that he is already pulling the lines. No more difficult to add one more when you're already pulling them. If he were to diplex the OTA line with a Sat feed from outside, He would have a diplexer outside, one at the tie in point, then a 2 way splitter, then another diplexer to tie it into the line going to the receiver, another two way splitter used as a combiner for the TV2/OTA), then another diplexer at the receiver, as well as another two way used as a combiner for TV2/OTA . Depending on the quality of the diplexers and splitters used at this point, you're looking at a signal loss of 15-20dB. That's not accounting for any cable losses along the way. That's pretty significant, even if you're using an amp somwhere. Not only that but if his antenna has a pre-amp in it, he'll have to run a sperate line from wherever the power inserter is anyways.