Hey there,
To be honest, I have never seen this deployed in the field, but then again you do not generally see VSS and N7K vPC deployed as parallel access switches. Normally you would use them in different locations, so would have the ESX box channeled to either the N7Ks or the VSS chassis
It would in theory work, but keep in mind that by dual homing your ESX boxes to both the VSS and the N7K you increase the complexity of the forwarding path and potential future troubleshooting. The other thing is with active/active, it will work providing you use MAC pinning on your N1K/VSwitch, however if you ended up with a loop on your ESX box you have the potential for introducing a network down. Active standby would not have this limitation, but you obviously lose useable bandwidth doing so.
HTH
Chris
