I think we'll use the radios for safety and to check in at designated times, once we begin regularly hunting away from each other. The GPS/radio combo seems perfect for such use, especially in big country.
For the example I gave, we were hunting in Ohio, but I hunt enough states that such use would be legal in some and illegal in others. Tom is right - I wouldn't even consider it if it was illegal, I was asking about "fairness". As much as I want to help my son get his first bow kill, I wouldn't feel right or fair using the radios as I described. I guess hand signals or a whistle could be used for the same purpose, but I wouldn't mind because of the lack of an electronic advantage. A fine line, no doubt.
My son is learning that "hunting the hard way" often means lots of fun/close encounters and not a lot of killing. At his age, I was more interested in a kill than the overall experience, to be honest. Sooner or later, it will happen if we keep getting close encounters.
Thanks for the input.