It says there that the offer *Requires cPanel*. So I'd hazard a guess that the cert is a billable option inside their web host control panel when you've also bought your domain name from them. 

Then the verification mechanism would be *"being able to log into the web host control panel that's associated with the domain name"*. And as far as security is concerned I'd say that's at least as good DV's verification mechanism of *"being able to receive mail for admin@hostname"*.