For tax purposes, "disabled" means unable to perform gainful work due to a condition that is permanent or is expected to last at least one year. Because of the focus on gainful employment, many people with medically recognized disabilities are not actually considered "disabled" for tax purposes.
If you file as disabled, there are not really any significant additional tax benefits, other than the ability to take early withdrawals from certain retirement plans without the early withdrawal penalty. There is a small credit for being disabled that you probably don't qualify for if you work, and you can deduct his medical expenses, but you could do that already.
As noted, you may have more of a legal problem, if he wants to retire early on disability you may need to consult a lawyer who specializes in that. Also, the "permanent" part may be a problem for you since GERD can often be treated with drugs or surgery. There's not much you can do on your tax return without a medical certification that he is permanently disabled and unable to work, and even then, the tax benefits are minor.
