So from a NAT and NSX perspective this design is great and will work. having a single interface for your traffic entering and exiting your ESG will allow you to run statefull services on that device.
The only issue I could foresee is with running dynamic routing over vPC. You may be fine since the vPC is layer 2 and your layer 3 endpoint is upstream from my understanding, but most cisco devices won't support dynamic routing over vPC.
Again, that's sort of aside from the NSX thing, but it's something you should probably look into. I know it's bitten me in the past.