@arijaycomet - thanks for making Tesla aware of this. They need more recent hardware; if they truly have no device they can test with the latest iOS, then that's a problem.
FWIW, I have iOS 8.1.2, Model S app 2.2, and Model S firmware 6.0 (IIRC). I do get sounds along with my banners.
1. Settings : Notifications : Model S - no sound option, but the list of apps in Settings : Notifications shows "Sounds, Banners" in small print beneath the app name. Clearly this was set at some point in the past (by me? default when I originally installed?).
2. Settings : Models S (i.e., settings for the app itself) has a "Notifications" entry that, as above, says "Sounds, Banners"; tapping seems to lead to the same Notifications page, but again, no sound option on either page (no surprise, at this point).
3. In the Model S app itself, there's a settings page. I have notifications checked for everything except "Charging Started" (timed charging = I don't want a wake-up alert ;-) ). No options for sound/no sound.
Some apps in Settings : Notifications show sound options and some don't. What they show (a toggle, or the ability to pick a sound) varies from app-to-app, so this smells like a bug on Tesla's part (perhaps triggered by an iOS update at some point). I don't remember what it used to have (on/off? select a sound?). Again, thanks to @arijaycomet for contacting Tesla.