Is it wise to give clients heads up about the service provider's disability condition?
Depending on the nature of the disability, it could definitely impact the quality of the service. Homes may not be wheelchair friendly. Dogs are often untrained/unruly, making controlling them difficult even for someone with no health problems. A petsitter should disclose anything they think may interfere in job performance.
Rover is merely a platform for sitters to advertise their services. Rover leaves the determination as to a sitter's qualifications up the client and vice versa. It is in Rover's TOS, Section 2.2, linked below:
As a client, you do need to read sitters' profiles. I would hope that a disabled sitter only offered services that he/she was capable of discharging. Also, it is very important to have a Meet & Greet with prospective sitters to determine whether they meet your needs.
FWIW, people in wheelchairs are totally capable of taking dogs on walks, although the dog needs to be trained to walk alongside, similar to a heel. So I'm not sure why you think a person in a wheelchair cannot be a petsitter.