Yep, we use AnyConnect for our VPN needs as well. But as most people don't have something like that setup for use outside of IT and just use your standard VPN setups, makes it more difficult for you average user to protect themselves. I know our guest wifi blocks all the consumer VPNs, even those that use OpenVPN or Wireguard. We get numerous complaints from both employees and non-employees and we just tell them the same thing everytime. VPNs are blocked on guest wifi, you can't use them.
You generally block consumer VPN's and DoH to force traffic to be compliant with "acceptable use" (filtering) policies (porn, malware, botnets...etc.).
I think that'll lead to more heavy handed filtering IMHO. Just blocking entire IP blocks rather than domains.
I'm not sure in the end, especially since the guest wifi is totally open with no password or anything on it, just a redirect to a page before you can use it after connecting to say your agree with the terms and policies and click the button to let you start using the wifi. Acceptable use policy and all that is already part of the page you click on to use the wifi. Funny thing is the old group that ran this area didn't block VPNs on the guest wifi while the new one that took over a couple years ago does. They also force everyone, employees and non-employees to use the guest wifi for personal devices and only registered corp devices are allowed on the main corporate wifi. They have no other wifi options available, which leads to some other issues that I won't go into here.
