Salt in high concentrations can kill yeast yes. So can sugar, though salt is so much better at it. You see both are hygroscopic, meaning that they suck water out of stuff. This induces osmotic stress to the yeast cells leading eventually to cell breakdown (aka death).
On lower concentrations salt will throttle the yeast fermentation producing a richer and more uniform crumb.
Adding the salt early or later in the process will have a big effect on your dough, but that won't be because of the way it messes up with the yeast. Salt is supposed to coagulate gluten proteins, in a sense it "stiffens" the dough. On various situations this should happen late in the process (e.g. see the "Delayed salt method" used for sourdoughs).
For pizza dough I'd add the salt early.