I was a Army Recruiter from 2003-2007. I've never heard of any such waiver. It there was one, it would need to come from the DOD or entry service. It would also be in your record if there was such a waiver.
I had a few Med waivers that the MEPS doc or Service Doc waived, normally bad breaks in bones, elevated BP, or childhood Asthma. The MEPS Doctor would have sent you on a consult to a MH doc for and opinion. None of my enlistees ever signed anything stating that they would not seek VA compensation.
It may not have been caused by service, but it could be aggrevated by service.