First, why does anyone want to shut off the OWB pumps when the OWB is in operation? If you have a DHWX wouldn't you want the pump running consistantly?
Why do you need a seperate thermostat? I have a heatpump with a mercury thermostat and they wired a aquastat to control my heating system. Here's how: (maybe it will give you another idea)
If my thermostat calls for heat, and the aquastat is below 160F, it turns on my heatpump. If it's above 160F, it only turns on my furnace fan. BUT- if I raise the temp on the thermostat more than 3F, it kicks on my heating strips (but not my heatpump).
Unfortunately I'm sure how this is wired in, since the dealer did part of the installation.
BTW: my aquastat is surface mount, not thermowell.