Yeup.
I've aqua jogged through many injuries. As long as he's cleared to do this (you do have to be able to hold your feet in position if that makes sense), go for it!
Have him ease into it (30-40min day 1, 40-45 day 2, 40-50 day 3, day off, 50 day 4 etc). My rule of thumb for recovery and easy training is take the time (e.g. 60min run) and multiply by 1.5 (therefore a 90min aquajog).
I also did lots of workouts in the pool. The sprinty stuff work well and neither did long sustained periods of effort (10+min). Keep the legs moving on the rest. And increase the number of sets. So a workout of 6* 4min with 2 min rest becomes 8-12 * 4min with 1 min rest. I saw never a puker during racing or training, but I could get myself to near puking point in the pool.
I'd say the hardest part about pool running is the mental effort it takes to continual maintain a decent pace and rate of effort.
Also- I HATE that aqua jogging belt. Too much belt. The best ones are just a skinny little rectangle. Make sure he doesn't lean forward and the movement is more like running 'a's (high knees) than a normally running motion.