Well, this game is NOT anything close to DRM-free. In order to do multiplayer (all I really want is hotseat) I need a separate Slitherine account, but I can't even do that! Every time I try to register, the game won't let me and gives me the message "unknown error."

You don't need to access Multiplayer to play Hot Seat. There is an option in the Settings menu to turn Hot Seat mode on for Single Player battles.

Having said that, you should be able to set up a completely free Slitherine account simply by creating a username on the Slitherine forums.

https://www.slitherine.com/forum/viewforum.php?f=477

If that doesn't work for you, please email support@slitherine.co.uk