Farage did reference Gps putting patients on 'a disability register' - I am not sure what he meant by that. There is no national register.
Some LA maintain a SEND register and a register for disabled adults - neither entitle a person to benefits. The registers are voluntary and help the LA plan services.
Our GP surgery does maintain a Learning Disability Register but again that is to ensure that the person receives the right sort of support - eg my child wont ever have capacity to follow medical instructions or answer questions, her guardian (me) has to be present and take responsibility for treatment.
Again not related to benefits. God knows why he'd suggest that would need to be assessed externally.
Either he has no idea what he was talking about or he was deliberately misleading for political purposes.