Is it possible to assign different DNS server to some specified hosts by the same dhcp server?

In the nework submenu/tab, instead of specifying the entire subnet as "address", specify the exact IP (with mask 32 or no mask) - everything else will be the settings that this particular IP will receive.

In order to ensure that a particular MAC will get that particular IP, you'll also need to add a static entry in the leases submenu/tab.