It's my opinion and experience that terpenoidal toxins emitted from Octocorallians have minimal impact on a healthy, balanced system. I keep soft corals successfully with a variety of SPS and LPS species, and have encountered no problems. When a soft coral is dying, however, I make it a point to remove him ASAP. Of course, this hasn't occurred in over 5 years.
Keep in mind that Octocorallians aren't the only things that emit terpenoinds. Species naturally occuring on your live rock emit a good deal of terpenoids - stuff like sponges.
Moral of my story is: if corals are healthy, terpenoids are the least of my concerns.