There seems to be a broad misunderstanding for how the rating system works for disability, especially amongst military members. I posted about this before, and will copy the response into this thread:
So, a few things.
First, this is not legal advice.
Second, for those of you playing along at home who are rated by the VA for a disability; that rating does not necessarily disqualify you for an FAA medical.
Third, as an example, if you have sleep apena and need to use a CPAP, the VA may rate you as high as 50%, but that has no bearing on whether you're meeting FAA guidelines on sleep apena (I'm pulling that off a blog post and not out of any VA documentation, but I imagine as a SWAG it's pretty close).
The VA will rate you BECAUSE you're using a CPAP to control sleep apena, and conversely the FAA may grant you a medical BECAUSE you're using that same CPAP and have your sleep apena under control.
These are separate issues that MAY intersect, or they may not. When in doubt, contact ALPA Aeromedical or your preferred vet advocacy group for accurate legal and medical advice.
EDIT: I'm also going to add, that if you go to the FAA's document on Guidance to FAA Medical Examiners, regarding question 18r, on page 33 of the document from 2006, it states: "The fact that the applicant is receiving disability benefits does not necessarily mean that the application should be denied."