I cannot, unfortunately, guess what the actual basis is that the Army is using for the discharge of your son and whether they think his injury is permanently disqualifying. Therefore I can't tell you what RE code or separation
code he will be given. I can though give you links to a couple of references that you can look at so that when he does receive his DD 214 he will know what the codes mean. For the RE code, he can go to: http://usmilitary.about.com/od/theorderlyroom/l/blcode3.htm For the separation code (there will be about 4 or 5 page of them) he will want to go to: http://usmilitary.about.com/od/theorderlyroom/a/code2.htm
My guess is that he will be recieving an Entry Level Separation and that his RE code will allow for reenlistment. Again though he will have to check when he receives it.
He will not be qualified for a Veterans' preference or VA benefits
if he only had orders to active-duty for training. If he was, however, serving on regular active-duty orders then he will qualify for some benefits but not all. There are a variety of benefits and they all have different requirements. You can see information about Federal employment and Veterans' Preference by going to: http://www.opm.gov/staffingportal/vetguide.asp
As for VA benefits, you can go to: http://www.vba.va.gov/VBA/ Each type of benefit, as I mentioned, has a different threshold for what a "Veteran" is.