I would think that as long as you have the Peppermint Shrimp in your display, you shouldn't need to worry about the Aiptasia becoming a problem for your tank inhabitants.
On the other hand, HN1 has a good point. Those nasty little buggers can get out of control really quickly. Perhaps you could put a Peppermint Shrimp in your sump??? I don't have a sump for my tank, so I don't know a whole lot about how they work or if a shrimp could even survive in there.
Hope that helps a little, and perhaps you can enlighten me a bit about sumps.