Connect to VMix call from basic license?

Are the VMix call limitations specific to *hosting* calls or using them at all? I'm looking to bring in a remote guest for an event, they use VMix but have one of the smaller tiers that doesn't include VMixcall. Would they be able to connect to a call that I host, or can they not use it at all?

Theoretically they can do ndi virtual input out of VMix to VMixcall.com if they need to in any case, I just want to know what I'm talking about before I get into pre-production meetings.