Hi,
So you have N7k acting as L3 with servers connected to 4510?.
Do you see the MAC associated with failing ARP in 4510?. Is it happening with all or few servers?. Just to verify if it is connectivity issue between N7k and 4510, you can configure an SVI on 4510 and assign address from same raneg (server/core range) and perform a ping.
This will help narrow down if issue is between server to 4510 or 4510 to N7k.
Thanks,
Nagendra