I think leaving the ram in depends on the breed and the individual nature of the ram himself. We left a Manx Loughtan
wether in with some ewes and he misbehaved horribly. We also tried one year leaving a (I think) Shetland ram in - he started butting a ewe viciously as she went into labour, presumably because she was behaving in a way he was not used to. We removed him and have not repeated the experimnent. Fergie, who is on this group, has kept a Soay ram in with his ewes year round with excellent results, especially survival of the lambs with foxes around. You can see his report on that if you search back through past posts in 'sheep'.
A Jacob ram could well be of help to the ewes in defending the lambs against foxes although when we kept Jacobs the ewes were well able to defend their lambs themselves
.
My concerns would be as follows: That the ewes could be stressed by rammy behaviour during their pregnancies and during delivery. By this I mean that primitive rams - and Jacobs still come into that category - have a greater tendency to boss their ewes around, keeping them in one spot and so on, which could affect in-lamb ewes badly. They could also go in for the butting of ewes in labour as my tup above did. I would also be concerned about a tup sharing the feeding given to ewes. Ewes need high protein feed coming up to lambing and this is usually given in the form of ewe pencils. However, these contain ingredients which should not be given to rams as they cause urinary tract stones which can cause an emergency blockage. Rams are usually fine with lambs once they are up, as far as my experience goes, but we have had a precocious Gotland lamb killed by Jacob
ewes, so I wouldn't risk it. If the ram is only the other side of the fence from his ewes he will probably be perfectly happy. If he was to be kept well away from all other sheep then that would not be fair on him.
Jacob ewe lambs could be fertile and mature quite soon after weaning so I wouldn't risk running them in the same field as their sire.
Overall, although I understand that you want company for your ram, I feel the 'against' points overwhelm the 'for' for continuing to run him with the ewes year-round