Hey Rob! Welcome to the UCS/VMware world!
VMotion is not a failover facility, it's a proactive maintenance facility. As such, you only use it to migrate "happy" workloads between "happy" systems on the same network.
Correct me if I'm wrong but it sounds like you are asking for a failover facility which wouldn't be VMotion but VMware's SRM - this provides an automatic way to failover VMs and re-IP them on a different subnet.
Check this link out for more details, and there's even a 60-day eval so you can prove it!
http://www.vmware.com/products/site-recovery-manager/
Let me know what else you need,
Steve