DHCP Relay / IP Helper Configuration Questions

I'm a little confused by the DHCP relay / IP Helper setup examples in the OS 10 documentation.  I have a pretty simple setup.  Primary WIN DHCP server is on VLAN 5 172.26.5.10, backup DHCP server is on VLAN 200 172.26.200.10.  It would appear that I simply need to use the "ip helper-address" command on each of the VLAN interfaces so they can relay DHCP requests.

Do I also need to configure the DHCP relay source interfaces to the VLANs the DHCP servers are listening on?  Is there any reason to configure the server override, and link selection through a virtual interface as the documentation describes?