If they take you by limo from vegas, then helicopter direct to the canyon, they're only operating in the area known as West Grand Canyon which is regarded as secondary to the traditional Grand Canyon visit. The latter is also known as South Grand Canyon. You can get helicopter flights over both, but they don't land in the southern area due to accessibility/depth. West Grand Canyon is much closer to Vegas though, so there are more of those tours available to the West.
You can do day trips by plane out of Vegas to the South Grand Canyon airport (which is what it sounds like RB referred to), then take a helicopter flight or other tour from the south as well, or just take a helicopter flight on its own from the south area too. It comes down mainly to time and preference.