Wanted to let you know that the team is looking into this, and they’d like to do some further testing on our end. The problem here seems to be that the health check can be surpassed because of the user agent string. Webex Teams uses the MSHTML operating system browser control for Windows authentication requests, and they don’t have the ability to set the UA.
A workaround you can use in the meantime if you don’t want Windows 8 allowed is to block on OS policy. Your users still won’t be prompted to download the Device Health App, of course, and they will have to be told “out of band” to load DHA. I hope that answer helps for now.
I’ll keep you posted as we learn more about this!