Vapor lock does not happen in the fuel rail or anyplace downstream of the fuel pump.  It happens in the fuel pump inlet. 
The main thing that matters for vapor lock is how far and how high the pump has to suck fuel.  Altitude can matter, but will not unless you are dangerously close to the critical pressure in the first place.  If altitude makes your fuel boil, you were within 10-15 degrees F of it boiling anyway.

Pulsation dampers are a fire hazard and should never be used.  Good quality pressure regulators will incorporate similar capabilities.  Typically, the fuel rail will be in between the pump and the pressure regulator.  The output of the pressure regulator should be to the tank.  You can think of the return line to the tank as being essentially a free flowing, no resistance path, so you can't build any pressure in that part of the system.  If the fuel rail were after the pressure regulator, you would have little to no pressure in the fuel rail - all the fuel would just flow back into the tank.

Things change in a returnless system.  In a returnless system, obviously, there's no return line to let the pressure out.  The capacity of the pump far exceeds the maximum flow of the injectors which is the only way out for the fuel.  So you can build a regulator which will maintain the appropriate pressure in the downstream area.  The drawback, at least for a rotary, is that you would always have pressure in the fuel rail, and leaky injectors can then cause flooding.