After getting ROTT '13 during the ongoing sale I figured there'd be tons of people trying out the multiplayer. But I see 4-5 servers, all empty. Is the MP dead, or is there an issue of some sort?

Not dead, but it's not many people either.
We are trying to establish weekly community events on Saturdays. People are also hanging in the Steam group chat for Rise of the Triad. If you go there, you can probably find someone for a multiplayer match.

You couldn't manage your server until weeks after the launch. Even then, there were login issues. By that time, the server admins (myself included) didn't bother anymore. I've got better things to do than nanny a promising game.