Assume you have DHCPSVR1 at 192.168.1.0 and DHCPSVR2 at 192.168.1.1. To split the 192.168.1.0 subnet between them:
1. On DHCPSVR1, create a scope from 192.168.1.2 to 192.168.1.254. Create an exclusion from 192.168.1.128 to 192.168.1.254.
2. On DHCPSVR2, create a scope from 192.168.1.2 to 192.168.1.254. Create an exclusion from 192.168.1.2 to 192.168.1.127.
NOTE: If you have the same scope without any exclusions, you can NACK the other DHCP server, resulting in clients being unable to obtain leases.