True is a correct logical rewrite for that Boolean expression.

Okay, maybe it's not a tautology. But it sure quacks like one.

boolean = ((X \[Or] Y) \[Implies]  Z) \[Or] ((! X \[Implies] ! Y) \[Implies] ! Z);

ruleList = 
 Map[Thread, 
  Map[{X, Y, Z} -> # &, 
   Flatten[Outer[List, {True, False}, {True, False}, {True, False}], 
    2]]]

(* Out[116]= {{X -> True, Y -> True, Z -> True}, {X -> True, Y -> True, 
  Z -> False}, {X -> True, Y -> False, Z -> True}, {X -> True, 
  Y -> False, Z -> False}, {X -> False, Y -> True, 
  Z -> True}, {X -> False, Y -> True, Z -> False}, {X -> False, 
  Y -> False, Z -> True}, {X -> False, Y -> False, Z -> False}} *)

boolean /. ruleList

(* Out[117]= {True, True, True, True, True, True, True, True} *)