Have not updated in awhile.
I've already proven it's very possible to keep butterflies and angels in SPS reef tanks. As evident by my collection of thriving SPS and butterflyfishes.
However, a rule of thumb for the SPS and butterflyfish rule is to ensure that the SPS is always healthy. If the SPS is unhealthy and dying, they will start attracting hoards of hungry butterflies and they will make short work of the dying colony in a few days.
Goes the same for all corals. If they are unhealthy, dying, injured etc, they attract angels and butterflies.
This milliepora shown here was injured due to the sting of my hammer coral. it started to STN from the base and this attracted the butterflies.
Here, a very rare paucifasciatus butterfly and a declivis is seen making short work of the dying SPS. I do not bother to save the coral because for me, this is a fantastic sight to watch and is exactly what happens in nature. The butterflies in my tank take turns to aggressively feed on the dying coral.
if the SPS is otherwise healthy and thriving, there is no reason for the butterflies to attack. the polyps remain untouched and the flesh of the SPS is unable to be torn off.