I don't think it is a protected characteristic. I haven't filled out a job application in many years, but it used to be a common question on the application. Protected characteristics are usually not found on applications, to protect from charges of discrimination.Isnt it a protected employment characteristic? You cant not hire somone because of their criminal record? (i know exceptions exist)
Personally, i wouldn't have a issue hiring one. (its probably cheap labour anyway that you can get away with paying minimum wage for)