Yes, Virginia, Tix does have a Tix_SafeInit() function.

Modules/tkappinit.c

@@ -59,9 +59,9 @@ Tcl_AppInit(interp)
 
 #ifdef WITH_TIX
         {
-		extern int Tix_Init(Tcl_Interp *);
-		/* XXX Is there no Tix_SafeInit? */
-		Tcl_StaticPackage(NULL, "Tix", Tix_Init, NULL);
+                extern int Tix_Init(Tcl_Interp *interp);
+                extern int Tix_SafeInit(Tcl_Interp *interp);
+                Tcl_StaticPackage(NULL, "Tix", Tix_Init, Tix_SafeInit);
         }
 #endif