J,
Toby, that's very odd. I went to that link and there's a place to
"sign in to groups.io" (not "sign into zendesk") - it looks like it's
asking for my groups.io account.
No, I think the confusion there is that it is asking you to sign in to the groups.io support area (at zendesk). A little bit as if on Y! or Groups.io you were being asked to sign in to a group name rather than the service as a whole.
I don't use Zendesk, so I don't know their setup. Possibly you need a separate sign-in for each support area?
Shal
Shal Farley