My quick read of the statutes says no...at least not for active duty retirement purposes. Again, I just did a cursory look at the statutes, but it appears that for regular length of service active duty retirements he needs to have 20 years of "Active service." My read, after looking at the definitions under those sections was that for those purposes, you need to have "active service" (which was active duty service or full time National Guard or Reserve service, which I think, in that section referenced AGR members...though, I did not dig as deep as I could have to have a full conclusion in my mind on this; in addition, there may be case law or other administrative materials that could indicate my thoughts are wrong on this).
I think he would be able to opt in to reserve retirement, though. Downside, of course, is that this would not pay out until age 60 (or qualifying reduction in years due to deployments).
I have thrown in a bunch of caveats here....this issue is fairly complicated, but my initial impression is that if disabled only due to Non-ILOD conditions, he would not qualify for the more favorable active duty retirement calculations (and therefore for CRDP on the active duty side). Though, from the backstory, I think he would probably be able to pursue active duty wrongful discharge claims and get to 20 years active federal service anyway.