If I use Vari-Etch on my pieces do I also need to use Liquid Luster to fingerprint proof the surface?

No.

Vari-Etch will fingerprint proof the surface of your glass either by etching the glass surface itself or from etching a sandblasted surface. 

Liquid Luster can be applied to a surface that has been etched with Vari-Etch for purely aesthetic reasons though as it creates a fantastic glow to those surfaces.