In my experience they don't really, except for teaching, where they sometimes get involved with some 'experience' scheme that involves a few weeks paid experience in a school.
I have not had much contact with their careers service, as like many other graduates I already had a job. I know that at the summer schools there was a careers advisory person there that some students had some interviews with.
You make a good point though. A lot of full time 'degrees' have placement years. There must be some sort of register of companies that offer this. I wonder if they would consider taking an OU student that is in their final year. Worth contacting the careers service.