OpenArena maps do have .aas files, I don't understand what its about with those aas files. I even tried custom Quake 3 maps with included .aas files, they don't work, too. What do I have to do to make bots work?
You need up-to-date area awareness system (aas) files and if you are using the botfiles available from the svn you need to re-create the bot's _i.c and _w.c files (The default_*.c files should act as templates) .
If you've done that then my guess would be that you have a configuration file somewhere that is telling the game engine that bots aren't enabled, find the line
"seta bot_enable "1""
and make sure that it is set as shown (0 is without bots).