It looks like I may have some free time this Wednesday and/or Thursday evening. I'll get a copy of WordPress installed, update the Nginx configs to route something to it, and get started picking out a decent themable skin then.
The WordPress users are going to be independent of forum users, though. I remember it being a challenge (although I did manage to pull it off) getting Mongo's user model to share auth with vBulletin. WordPress is famously modifiable, but because of the aforementioned security fears I have about vB, I'd rather not even introduce the possibility of cross-talk.