Hi,
PlayMaker is a framework, and as such it has a small impact on performance, but we have to define what "impact" means here. It's likely that you'll never experience any issues with PlayMaker itself when you will profile your game, you will find that mesh, textures, shaders and wrong logic flows will affect performances very badly if you don't optimize them properly. PlayMaker "only" brings on the table a different way to organize and define your logic and behavior and as such doesn't really have any impact at all compare to all the things that can go wrong...
now, In the Unity editor, you will see some performances impact when you have the PlayMaker Editor open, and that's to be expected somehow, just like hacing the Unity Inspector open affects performances too. Typically, I have a special layout with just the game view to actually test in editor with the least impact from the editor tools. And as always, you MUST run on the device to get the proper performances of your project.
Bye,
Jean