Official info straight from a Disney CM RE: Guests with Disability Parking Placards
To avoid the fee for the parking, you can register your car with security or front desk. You must have a valid disabled parking placard to park in the accessible parking areas. As long as you do this, there will be no parking fee charged to the guest(s).
If the guest doesn't qualify in their state for the disability parking placard and have it on their person at check-in or the security gate, which it should be hanging on the mirror or evident on the car's tag, then the guest will be charged the parking fee. It's that simple. Not to say that other folks with disabilities shouldn't necessarily have the same rights, but at the same time, guests with disability placards are already, typically, not absorbing every single handicap spot in the parking lot on a daily basis either.