VPC toward Dell Chassis is UP but i cannot ping dell side.

Hello, I don't familiar nexus devices but might be helpful this articles. You can use the show vpc consistency-parameters command to verify that both vPC peers have the identical type-1 parameters 

You can use the show port-channel summary and show spanning-tree commands to verify that the VLANs are allowed and active on both sides of the vPC 

https://dell.to/3R8GVwY