the biggest reason triggerfish are considered not to be reef safe is because of their tendency to move rocks around (thus knocking corals and anenomes off the rocks), not because of a direct threat to the anenome or coral. so maybe you could try it and return the anenome if it doesn't seem to work out.
by the same token, triggers DO eat snails and urchins, so check to make double sure that the anenome isn't on the trigger's menu. I don't believe it should be though.