I mean without the use of modding or the console command, as I'm playing on my PlayStation 3. I ask this because I would love to see the Whiterun guards really wailing on the dragon along with my help. just think it would be epic seeing a mass of whiterun guards firing at it in a combined effort. If you know for certain, that would be really helpful c: Thanks!
Dragon attacks and other types of random encounters will only happen when the player is around to observe them. Dragons will occasionally attack cities like Whiterun when you enter the city. That said, dragons have no particular grudge against the player after they have spawned, and are likely to start fighting nearby NPCs. So yes, it is possible to see half the city guard fighting a dragon within city walls.