Unfortunately, berghias will not eat them. Bummer. A butterfly is a great way to get rid of the pest however in a smaller tank, a butterfly may not survive long.
You can take out heavily infested rock, pluck/scrape them, then take a lighter to the base area and heat that area up. I had to do that when I had a few majanos. My battle has always been more with aiptasia. If only zoanthids and sps grew like aiptasia my tank would be awesome!