Wrestling got me started in martial arts. I wrestled from 5th grade to my sophmore year in college. It helped make me the person I am today. In the Lansing Michigan area wrestling is a big deal and most of the better athletes in our high school were wrestlers. I took my first Judo class to help improve my throws for free style wrestling and Greco. I had a great fall this last year since my two boys 5 and 8 wrestled in their first tournament, one took first and the other took 2nd. I ran into old friends, coaches, and parents who were now grand parents of wrestlers from my hight school years at the tournament. I had forgotten what a large family the wrestling community is and how much fun I used to have. I really have to watch my pushing the boys but Im proud to say that they were the ones who suggested that they start wrestling. I can also say I got the chance to learn from Dan Gable at a camp at Olivet college. I learned an inside switch that I used to win more than one match from him.
I think that BJJ will most definitely help his wrestling. Just make sure that he know he can't be on his back when he wrestle. Also, you are right....he needs to work on takedowns 24/7. The three I recommend are single leg, double leg, and fireman's carry.
Hip throws are allowed in h.s. wrestling. The fireman's carry is not used in BJJ alot. It's mainly a wrestling takedown but thats why it would work so well in sport jiu jitsu. The fireman's carry is where you shoot in on your opponent and one arm pulls the opponents arm over your neck while your other arm does a high crotch and you flip them over your head.
After a few years of both wrestling and BJJ he'll be really good for jiu jitsu competitions because they practice mostly single and double leg takedowns and thats about it. Once you take an opponent down thats when you go right for the mount to finish him with a submission or ground and pound. Usually the jiu jitsu person is shocked or stunned because he's not used to the wrestling takedown and gives you enough time to take the mount position. Have your son learn as many wrestling takedowns as possible.
You should have him work on stand up fighting as well. Then he'll be really great and be able to defend himself both on the ground as well as standing up. He'll have all bases covered so to speak. Nobody would be able to pick on him in school then.....lol.