Hey Mike, Thanks for asking that question! Had you not, I would still be under the wrong impression of what a corals mucus contains. Turns out it is a rare event that such mucus would contain nematocysts, and if so, its doubtfull the cell could survive long and would not be in sufficient quantities to be of concern. I did however learn a great deal about the role a corals mucus plays and was amazed at just what goes on within and under a corals mucus layer(s). The only real concern with mixing the aggessive species in with gentle species is one of actual physical contact through sweepers and/or mesenterials.
Again, thanks for making me think! Check this out if you haven't already done so.
The Silent Sentinels - the Demise of Tropical Coral Reefs
Chuck