Many people who work in OH do not work in a "department" as such, they may be a lone practitioner in a company for example, or work in a peripatetic position for a large provider. Likely then that these people would be "managed" by disparate people such as HR or account managers. I am also aware of companies that offer OH services that have (eg) a psychologist as the manager 
 
Like Anne I would think it preferable that the function is managed by someone who understands what it is all meant to be about - but this  is not practical/possible  in a lot of circumstances. Actually I would a lot of sympathy for someone who was "drafted " in to manage an OH dept with no OH understanding as I am sure they would feel very vulnerable, have a lot of conflicting issues and would generally feel up the creek without even an OH paddle.
 
It would be very different if that non OH manager was acting as a mentor/offering practise placements I would suppose, but others would be much more qualified to comment on this than me