I am looking for a vacuum pump, and was told that using Cactus Juice without a "cold trap" would void the warranty, that the vapors would soften the plastic vanes. is this true, and should I look for a particular brand / type of pump.

Unfortunately, you are being given bad information.  Cactus Juice does NOT have any "vapors" that are getting into the pump.  Cactus Juice is made for full vacuum applications and will not boil (turn to vapor) under full vacuum unless the temperature of the resin is above 93° F which is above the use and storage temperature of 85° F to begin with.  Also, good quality, made in USA vacuum pumps such as JB pumps do not have plastic vanes to begin with.  Some of the cheap imports do, though.  Damage to the vanes on cheap pumps is NOT caused by Cactus Juice.  It is typically cause because folks did not follow the recommendations of properly drying their wood to begin with.  Any moisture left in the wood will be boiled of of the wood under deep vacuum.  This moisture will have sap components and other volatile components that can gum up a vacuum pump.