THis is how I see it-
To add mass you have to have coloric surplus. Period. If you fudge on the side of more than you can use for energy and building muscle, some will be stored as fat. You'll pretty much have to accept some fat gain when adding lean mass. When you add cardio to the mix it's just a way of skewing the calories in vs. calories used equation. So you can overeat enough to gain mass and put on lots of sloppy weight, then do cardio to make up for it (which seems daunting to me) or you can dial-in your diet better to be a bit above maintanence in order to gain lean mass without too much sloppy weight and ditch the cardio.
Of course it's good to do cardio for the sake of your heart, but as it relates to gaining/losing weight, it always comes back to the difference between calories used and calories consumed.