The only time I have left a wether hogg in with lambing ewes it proved to be a bad move and we had to get him out. As In the Hills found, the hormone smell confused him, he forgot he has been castrated but knew he was frustrated so as soon as the ewes started the birth process he was in there stopping them from lying down by pawing and butting and generally trying to mount them (we put him in with the tups where he found just what it was like to be on the receiving end of all that attention
). He was a Manx Loughtan, the ewes were Hebs and Shetlands.
Ewe hoggs on the other hand are usually fine in the birthing field and I believe they benefit positively from seeing the whole process, so when they lamb the first time themselves they know what new lambs are and what they smell like, so they don't get a terrible fright when they produce one themselves. Sheep love to be in family units and soon team up with the lambs.
The only exception to this I have found is with Soay hoggs - little b^663r$ had to be put out.