Being the precursors (or ancestors?) of vampires, Nightstalkers shared the ability of most vampires but didn't have as many vulnerabilities as they do.
For example, although sunlight which instantly kills vampires and burn them into ashes certainly could inflict some damage to Nightstalkers, the regeneration ability of most Nightstalkers would be compensate—or indeed overcompensate—for the damage sunlight could cause, which meant it wasn't lethal to them.
Additionally, the rumor that anyone bitten by a vampire would become one was mistaken.
Vampires were basically Nightstalkers of diluted bloodlines. However, when the gods wiped out the Nightstalkers, the curse they forced upon the Nightstalkers extended to the vampires, forcing them to shoulder a great many vulnerabilities and curses.
