Yes, Virginia, Tix does have a Tix_SafeInit() function.
diff --git a/Modules/tkappinit.c b/Modules/tkappinit.c
index 56556c7..392269b 100644
--- a/Modules/tkappinit.c
+++ b/Modules/tkappinit.c
@@ -58,11 +58,11 @@
 #endif
 
 #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
 
 #ifdef WITH_BLT