Not exactly. In a BFU (Before First Unlock) state after a reboot, update, etc. you need to unlock the owner profile before switching profiles. Also, when I switch to a secondary user, while I don't see the ability to change DNS settings, I can set up a VPN. I know there are new VPN / DNS functionalities coming in the next update but I'm not positive how this will affect things. It may be possible for the user to simply setup a VPN and bypass any DNS filtering you have.
If you're pursuing this workflow for like a "parent restriction" setup for a minor, it's possible. However, it doesn't matter how many barriers you attempt to put in front of the user, there will always be a workaround if they're at all tech savvy (aka know how to use Google).