It depends how your unbound is configured. In my case, I have unbound running on my laptop configured as a recursive resolver; i.e: it will not query the DHCP provided DNS.
In networks with captive portals, the DHCP provided DNS will have a record for a URL where the user has to enter credentials or at the very least agree to the terms and conditions. Very often though, that URL only resolves locally, so in my setup the captive portal setup doesn't work seamlessly.
