Scout Tenting – Like pretty much everything else in Scouting, there are the official rules and then there is the way that individual Scout units run things. So regardless of the rules, you need to check with the Cubmaster of his Cub Scout Pack, and ultimately the Scoutmaster of his Boy Scout Troop, to see what the local practice is. If he's really a Wolf Scout (7 yo), then his Boy Scout experience is far enough in the future that the Troop practice may well change before he gets there, so the only thing that matters right now is how your Cub Scout Pack does things.
The official rule for Cubs is that the boys camp with their families. In Packs I've been associated with, this has variously meant that the whole family is in one big tent, that the family can be in multiple tents on a single campsite, or that family adults are in their own tents while boys are in shared tents or cabins. The only thing you won't find is boys in a tent/cabin with unrelated adults.
If there's a rule that Boy Scouts can't be in one-man shelters, I've never run across it, and I know many Boy Scout units that don't enforce it.
Also keep in mind – in most Cub Packs there will be a maximum of 2-3 camping opportunities in a calendar year. Depending on how much you get out with your own son, you may control the majority of his camping experience. So do whatever the heck is right for you.