no guarantees on the parking there short of having an ADR at Jiko or Boma. but if you tell the guard you want to look around, it might be possible. getting there by disney transport would be a non-issue.
if you walk through the lobby and go out the back, you can go to the main viewing area, arusha rock. there are also other viewing areas, including the one by the pool which is usually used for night-time viewing.