I haven't seen customers enable fabric failover and vMotion, but it sounds like an interesting design. Was it CSE or Advanced Services Architect who recommended it? It might be a new practice, but I don't see anything wrong with it.
Whatever you decide, as long as the VM traffic is on separate vNICs, instead of using fabric failover, that will save the Fabric Interconnects from having to process the gratuitous ARPs necessary for the VMs if the vNIC does fail.