I was playing Assault mode (can you play on any stage other than Mos Eisely?) and during one game I issued a command to another hero, and even though some soldier reported that the hero works alone she (think it was Aayla) ran by my side. Groovy, me thinks, and together we kicked ass. Is this normal in Assault mode or some bug?

I noticed that bug as well. In Mos Eisley, on Assault, the heroes have the same characteristics as standard soldiers so you can use squad commands, but as they're heroes, it says by default "Heroes are most effective fighting alone" In answer to your question, yes, you can use squad commands with Heroes on Mos Eisely - Assault, and no, that's the only ground based Assault map.

I've never tried that. I will the next time I play that map. In answer to your other question, you can play other assault modes, but you need to download mods in order to do that.

For PC... the +123 MOD (http://starwarsbattlefront.filefront.com/file/123;66282) will allow you to play Hero Assault on any shipped map of the game. It adds a total of 123 game types to your Battlefront 2 game. Hero Assault on the shipped maps is just some of the neat stuff it adds. Installation of this mod doesn't change any files originally installed by SWBF2. It simply is deposited into the Addon folder:
C:/Program Files/LucasArts/Star Wars Battlefront II/gamedata/Addon