They'll work as a team, bunching and herding the pigs, circling the herd, keeping them together. With my minimal electric fence, the smaller pigs slip out, and the dogs are pretty clear about the rules: If the pig is outside the white electric fence, it should be back inside. They patrol the open areas around the current field and take their job very seriously.
I don't know much about training herding dogs. I think it's time I looked for someone to take some herding classes from. It'd be useful if the dogs could cut a pig out under my direction.
I've been slowly moving the pigs into a three acre wooded area on my property. The goal is to have them clear some of the area so that they can have shade in the summer, and I can get more use out of my land. So far it's working well.