How heavy is the Ram lamb? How are you managing them now, I really wouldn't keep him separate for a month.
I would put the lamb in and see what happens, he should cover them, particularly the 2 ewes, they will probably 'show' him how to do it.. The ewes might not like him though if he's small or if they chase him off he might be too scared to cover them when the time comes, or he might not be interested in the ewes at all..
If you can fine a Raddle to fit him its always good to know if he's done the deed rather than wait till spring to find out.
I think its worth doing, a lamb is a lamb after all and I suspect that it will be easier lambing a purebred Ryeland lamb than one crossed with a larger breed, so should be good experience too.