Lots of things to unravel here.
First, the concussion background is always a concern. That said, most of the concussions I've seen in wrestling, either as a wrestler or a ref, are pretty random things. It's impossible to predict when a wrestler will suffer a concussion, and as such, there really isn't much you can do in advance to protect a wrestler. Having had a prior concussion does put your son at an increased risk of another concussion. But if he's not experienced one for two years (I'm inferring that; not sure if it's correct), then it's likely that his vulnerability isn't much greater than someone that hasn't had a concussion.
In terms of wrestling up, there is no hard and fast rule. There's a lot of value for lower weights to wrestle up in practice, as they have to be crisper with their execution to get a TD. On the flip side, there is value for the higher weights to wrestle down, as they usually (not always) have to deal with a wrestler that has more speed than they are used to, which helps them with their footwork, keeping good positioning, and their defense.
167 wrestling against a 225 -- that's not too bad, provided that the 225 is careful with your son's back, and will stop immediately if your son taps. 167 wrestling against a 290 -- you have legitimate reasons to be upset. Just be careful about how you raise the issue with the coach. A polite, relaxed conversation may accomplish more, and also won't embarrass your son.
Embry-Riddle is, if I recall correctly, in Florida, so I'm guessing you're in Florida. If that's the case, then the first day of practice that is permitted by the FHSAA is Nov. 8. As such, I'm guessing that this is offseason practicing, that is supposed to be more informal than normal practices.
The upper weights traditionally have problems with numbers when football is still taking place. It happens in PA as well.
Have a polite conversation with the coach, express your concerns, and see if you can come to an understanding/agreement as to the upper limit, in terms of weight, that your son will wrestle in offseason practices.