you probably found your answer by now but from my experience there is nothing special about a "swim jig", Its just a technique to use with a jig. booyah calls one of there jigs a swim jig but ive had some explosive hits swimming a normal jig over grass or brush. Maybe there is a certain time to use it but i usually end up doing it anytime i have a jig locked in my hand and it will pick up some extra bass that want a different look.