Pihole docker and dns set

Hello guys, one quick question. Now I have set pihole on synology docker, pihole set to manage dhcp, all dhcp servers disabled on routers. Do I also have to set dns's of all routers based on pihole address? Don't know why but long time ago I read (dreamed?) that setting pihole as dhcp manager is enough. One other thing, if I mess up the container or the synology is not running, all devices will stop getting ip adress and that is normal but there is any solution to this without getting another failsafe device ?