From what I have experianced in the voice and a little in the Vo/IP, yes the call attemps can have an impact on the switches processor load.
I would also assume that depending on what type of switches/routers the calls are processing through will greatly determine the threshold of when the switch/router may be impacted by heavy/large call volumes.
I also don’t know of any switch that is truely “virutally non-blocking”. And I have experianced a switch almost shut down because of call volume to it.