I've never heard of peps going after bta's. Other nems yes but not bta's. I've had several batches of peps and never had an issue with them going after bta's. I now have rock anemones in addition to a bta so when and if I do get aptasia I'll try berghia.
I’ve got a few peppermint shrimp in my BTA tank that were there before the BTA’s. They haven’t bothered them at all, and I have like 12 BTA’s in there of various sizes.