1. you can setup DHCP server to use specific ports/ranges for RPC. RPC itself uses port 135 for Discovery, where it will offer a services on specified ports. That means, you have to have port 135 open and then your specified range on the Firewall and for example remote MMC console or IPAM should be able to connect over there.
2. Definitively you dont need to have SNMP enabled on DHCP.DHCP server can be monitored using ICMP as an IP Address and RPC is used to download all Scopes stuff. SNMP is used basically to get some additional information for IP Address (HostName, MAC). And you may have also Neighbor scans, which asks specified devices on your network using SNMP for their ARP table records to find active hosts and MAC addresses.