One of my consulting customers pointed something out to me that I hadn’t known. IP helper (now DHCP relay) works differently on the Nexus 7000 than on the 6500. The N7K imposes a VACL to filter local DHCP broadcast traffic, under the assumption that you’d be using DHCP relay when there is no local DHCP server. So if you are planning on using a local DHCP server with the DHCP relay (former helper) address providing fallback to a remote DHCP server, you need to put in a DHCP relay line for the local server as well as the remote one.
For full details and a configuration example, see https://supportforums.cisco.com/docs/DOC-14753.
Here is my version of the configuration example provided:
interface vlan 10
ip address 10.1.1.1 255.255.255.0
ip dhcp relay 184.108.40.206 ! remote DHCP server
ip dhcp relay 10.1.1.2 ! localDHCP server