I don't really understand how you think the game could work if the host didn't know where the prize is? They'd keep accidentally revealing the prize, and then asking you whether you want to switch to the other remaining door, at which point... what's the point? The game is over.
I've not usually seen it explicitly stated like this that the host knows, but it's always seemed obvious to me that they must.
I worked for an epub firm that used a similar approach a while ago - we took PDFs and produced Flash (yes, that old) versions for online, and created iOS and Android apps for the publisher.
I've come across most of the problems in this post but the most memorable thing was when we were asked to support Arabic, when suddenly all your previous assumptions are backwards!
Imagine all you have is a password, and I come along to register, attempting to set my password to "hunter2". Turns out someone else has already used this. Do you allow me to continue or tell me the password is already in use? If its in use - great, I'll just log in using that other guys account!
Of course, you could let the site specify the password, which would work if they're long and random. But social security numbers are neither of those.
I've not usually seen it explicitly stated like this that the host knows, but it's always seemed obvious to me that they must.