is it possible to set DHCP's ip address to be the same as DNS server ip address?
That question doesnt make too much sense. If both roles are installed on the same server with one NIC, that NIC will only need one IP address. There is no need to have a server with more than one NIC or IP address to be bound to different networking services running on the server.
Generally, if the server will have both roles, you should assign a static IP address to this server. On your DHCP scope, you will include many options, one of the options will be the DNS server(s). you will use the IP address of this server in that DHCP option so that when your DHCP clients negotiate a DHCP lease, they will point to this DNS server for DNS services.