Anthony A. said:so are most all independent sprinkler controllers function this way... ie. no override?
Your question reminded me that there IS an override shutoff input on most sprinkler controllers for a rain sensor input. If that was wired to the omnipro with another relay you could shut off the Hunter. Not sure if most controllers will shut down immediately or wait until the end of the current cycle - I would think it would be immediate but something to check.
My plan is to go with something like opensprinkler but I would like to have a local control panel so it can be run like a conventional controller if desired - easier for other members of the house. Maybe something like opensprinkler on a raspberry pi combined with lcdproc - it supports an LCD and keypad.