So you're thinking about doing a wraithlord for the monochrome competition? I love that model, so may neat possibilities.
Yeah, I always thought the historical vehicle/monster category was poorly named. In this case, monster means a guy on a horse, though I'd love to see someone argue with the judges to get their Idi Amin or Hitler figure entered into the category. Just so you know, the Bay Area Open is a Crystal Brush Qualifier, but it uses different categories. There's no fantasy, sci-fi, or historical divisions. Assuming they use the same rules as last year the categories are:
Single - any normal sized mini under 54mm
Large Single - any single figure 54mm to 1/6 scale (not including vehicles or walkers)
Squad - themed group of at least 3 minis
Vehicle - Anything that can be ridden, driven, piloted, or flown
Diorama - any scenic layout mounted on a display plaque (can include duels)
The judging is on the open system, so gold, silver, and bronze are handed out based on the standard of painting (not just a single 1st, 2nd, and 3rd in each category). From all the entries the judges select a best in show that wins their prize package (last year it was an airbrush and complete set of minitaire paints). The organizers of the gaming tournament (not the painting judges) select the winner of the Crystal Brush Qualifier. So Best in Show and the Crystal Brush Qualifier can go to the same figure/person or to different ones.
Last year the painting competition was run by the Draconic Awards (they're doing the Las Vegas Open this weekend too). I'd expect them to do the BAO this year as well, so you can check out their website for more info on the rules and format.
http://www.draconicawards.com/index.cfm