Do I need to use gongfu style for an oolong tea?

No you don’t need to, but you may. Gongfu style is one way to interpret a tea. It is most popular in oolong regions because it was the quickest way to make an enjoyable sip of most oolong teas in the beginning. Perhaps it still is. However, the full taste profile of many oolongs can be achieved in other styles too. Infusion really is part of tea enjoyment. Finding out a best way to bring out the best of a tea is part of it.