Joining two Z-wave networks / Vivint

[CPRail1]

Hi Guys, 

I've been using Insteon and ISY for quite a while but very much a newbie to the Z-wave side. I got into it to integrate Somfy blinds into the rest of the automation.

Separately we have a Vivint alarm system, most of which is based on 2Gig Z-wave modules installed by Vivint. 

I'm thinking that having everything running as one z-wave network would be the best for reliable communications, particularly to my few new Z-wave items that the ISY cares about, rather than adding otherwise unneeded  Z-wave modules or repeaters. Of course having the ISY be able to react to any 'Vivint' alarm items opens up some cool play ideas. 

Researching the concept of primary and secondary controllers on one network would seem to say that I could have the Vivint control panel ( a 2Gig product I believe) and the ISY exist on the same network. 

I'd appreciate any thoughts on this and would particularly love to hear from anyone who has done this.

Thank you, Peter