Welding exhaust is easy, Yelo hit it right though make sure to disconnect the battery before you start..... If its a crack, weld it, its its a hole or the metal is deformed at all..... Replace it. Any reputable exhaust shop can do it alot cheaper than a new preformed pipe from the dealer.
A tig wont be putting brass on it, but Tig would be ideal for alloy repairs like this. But if your gonna have it TIG welded, then itll need to be super clean inside and out... IE itll need to come off. If he is good with an oxy acetalyne torch, braizing would be the way to go, not as hot as welding, and dont need inside and outside super clean.