Thanks again for the quick response. The documentation of the module is still proving difficult to get - and still trying. So far our contact has only given us the “it has a simple Normally Open / Normally closed contact option. so a simple relay card”. I know - not always the best to go off of, but they are using our questions as an opportunity to get us to use their monitoring service 
The property is a very large residential property that is not required to have a system at all (in this city only commercial & multi-unit residential fall under the required list), but had the components donated for an over-the-top coverage scenario.
Based on what I know of the relay module is it has 3 relays you can use, but not required to use all 3. The alarm relay, which activates during alarms. the other 2 relays are activated for “supervisory” or “trouble” situations - think along the lines of shorts detected in the wires, low/replace battery, loss of power, etc.
In the option you listed, we would probably go with 3 of the sensors, one for alarm which would be programmed as a fire type zone, and the other 2 would be programmed to send a notification of the trouble/supervisory situation but not set up as a fire zone or of the type to trigger anything with the monitoring. I actually do think the option you listed would work, the only worry i would have is if the signal is the right strength (wrong word…i know) to actually trigger the sensor correctly.