"how ridiculous is that statement"
"Yes, salt, if unknown or per-user, will prevent Rainbow Tables"
Way to contradict yourself! This discussion is now over.
No, you imply that it can't be in a RT because of its "unique salting method", like if two computers would compute a different hash...
However this would be perfectly RT:
crypt("pass","$6$rounds=5000$myeverydaysalt$");
And unknown or per-user salt will prevent RT
on every algorithm and not just SHA512