you should be able to run dhcpd on your own subnet w/o causing problems to any other dhcpd servers on other subnets that service you. to be safe, you can also disable any dhcp helpers on your switch ports that service you subnet.
This is only true if your network is on a seperate vlan or physical network. Multiple subnets can coexist on a single vlan, in which case you would surely cause issues on the LAN.
You could also configure a dhcp server to respond only to known macadresses.
Ger