They can survive at pH 8.0, but incidence of things like mysterious diseases and short lifespans are much more of a problem. A healthy neon lives 4 years or more. While you will often hear people say they kept them in hard, alkaline water without any problems, rarely do their neons last more that a couple of years.
If you have hard, alkaline water, consider either the tetras naturally adapted to hard water (for example x-ray tetras and red-eye tetras) or opt for things like rainbowfish and livebearers that will prefer hard water.
Cheers,
Neale