Well, the Animal Welfare codes call for all herd (or flock) animals to have company of their own species, so it'd be best if he had a wether or two for company as well.
As to grown sheep with cattle, shouldn't be a problem, so long as the tups don't go for copper-rich licks, of course.
We try to keep lambs away from cattle, having had the odd injury or worse in the past.