Would this work to integrate into an existing wired security system?

All window and door contacts are grouped into zones and then wired back to the bus on a panel. I was thinking of tapping into the two wires that would come back for each zone and use a z wave door/window sensor that allows for hard wiring and the result would be a zwave sensor acting as a zone wired to the group of windows.

I think this would work

Yep. But also see the ST_Anything thread.

Yes but requires a more complicated setup through Arduino or even the rasberry pi route

But, you can hook multiple sensors to a single Arduino. You would need to buy a ~$40 device for every door sensor you want to connect.