I think for a wheelchair basketball team, they have a points system, you need a certain level of overal disability to make your team be valid. (Although I might be thinking of a different disabled sport?)
a policeman cannot go on the beat in a wheelchair. They tend to do office based jobs and interviewing etc. Not sure if they become policemen whilst disabled. I know the ones who are in wheelchairs became disabled after being employed.
Re basketball - I imagine you have to be pretty adept at using a wheelchair to play basketball in it. So even if you do not have to show evidence of a disability the chances are that you have built up that skill by using it long-term, ie through needing it because you are disabled. Whether or not people who have used wheelchairs in the past continue to play wheelchair basketball even if they are no longer using a wheechair for mobility purposes, I don't know.
Police - they'll have some sort of Equal Opps/disability policy, or ring the Disability Rights Commission, they should know. I cannot remember whether the police force is still exempt from the Disability Discrimination Act, tbh.
According to the police website "The police service welcomes applications from people with disabilities and will do all it can to make reasonable adjustments, which will allow disabled applicants to do the job.
Please let us know if you have a disability and the type of adjustment, which you might need to enable you to apply for and do the job." I reckon it would be virtually impossible to get them to agree to a beat job in a wheelchair. Mostly because everyday environments are so inaccessible.