In my own working copy of the guilds file, I got a quite good balance of guilds even for AI factions. They tend to get quite a lot of horse breeder and order guilds in particular and some sword and merchants guilds. Of course also the occassional thieves guild.
Haven't seen an assassin guild or explorer guild with the AI yet in my set up, but thats likely due to the AI hardly ever training/using assassins or if they do, they have other guilds already.