Maybe we just have a super natured jack, but Cee Cee stays in with our 3 jennys 24/7 365....
We kept him apart for a year (we did not think jacks and jennys would get along). The people we bought him from had him in a separate field so we figured it was because he was mean to the others. He always seemed so sad though. So we put them all in together and they got along super. I wish we had attempted it sooner, but live and learn. He had a mule friend in with him but they never really hit it off. Now we don't even take him out when the jennys foal...they just turn and look at him and he keeps his distance. It is like they are his little "family".
So I would say try it. It might just work out super!