The Idaho Grape is a nuisance and becomes a problem in tanks, like GSP. Personally, I killed all of mine a couple years ago and don't regret it a bit. If you can keep the Monti isolated from the reef structure great, but Idaho Grape will completely encrust around SPS........nuisance coral, IMO.
I'm not sure what it is classified as, but IME it encrusts and plates (like a cap).a little off topic, but is Idaho Grape an encrusting monti , or a monti capricornus?