Variable Nozzle Guide Vanes do the same job as non-variable ones, they are just optimised for a greater range of conditions so they're characteristics will be the same. 

[From this article][1]:

> They direct the airflow onto the turbine blades while at the same time converting pressure energy into kinetic energy. 

They will accelerate the flow and therefore reduce the pressure at the vane outlet.

There is also [this blog][2], which is a very good and informative read about gas flow in a turbine. 


  [1]: http://encyclopedia2.thefreedictionary.com/nozzle+guide+vanes
  [2]: http://aerospaceengineeringblog.com/jet-engine-turbine/