I keep three kind of Caulerpas in my refugium (two sprouted from my live rock, the third I got as a tiny piece on the back of a Mespilla globulus), I have never had any problems with the "toxins".
Remember that the stuff that was invasive in the Mediterranean sea (C. taxifolia) was actually toxic to the local species, but species coming from the place where these Caulerpas are common are actually immune to it...
As a side note, the species considered as dangerous are the feather-types (C. taxifolia being one of them), C. prolifera is not a problem. It is a cool algae and if you have a fox face they will love it as a snack.
The main issue with keeping Caulerpa in a refugium is that they can make their way to your main display, and then it is impossible to totally get rid of it in my experience (my fox face eats the sprouts, but they keep coming from deep inside the rocks)
