Oh that will work.
Yes most leathers, and some others, use toxins to deter other corals from overgrowing them (slows their growth), but it effects mostly SPS corals, softies should be fine, and as long as you use carbon 24/7 you should be fine. One of the biggest offenders of leather corals is Sacrophyton (toadstool) corals, they usually have the biggest effect on other corals in close proximity or down stream from them. Sacrophyton has also been shown to actually make Xenia grow better (Anthony Calfo pers. exp., and others) in captivity. This is still unknown as to why exactly. Overall mixed tanks usually do pretty well as long as you do frequent WC and run carbon the toxins don't really build up.