Uplinking switches between companies

Hi Reddit,

I work for an MSP and I had a customer of ours bring up an interesting scenario that's got me a bit stumped. They currently use their own phone system, but they are going to migrate to their parent companies Cisco VoIP solution. They are located in the same building, different floors, as their parent company and the solution they want is to uplink their switch to their parent companies switch. Uplinking switches between companies is something I've not came across yet, I can't think of any reason that wouldn't work assuming they aren't using any overlapping subnets (excluding voice of course) so I wanted to bounce the idea off reddit. I always configure my switches to be VTP transparent so there's no risk there, nothing else comes to mind as potential roadblock. Thanks all.