I started HP Mass about 8 weeks ago in conjunction with low carb/reduced calorie diet. I thought that the low reps would be good for retaining muscle while trying to lose fat. I was very surprised to see that after about 5 weeks, my triceps, chest, and shoulders were noticeably bigger, even with fewer calories. My legs also seemed to grow with all of the prowler pushing. I eat very low carb all day and train around 8pm. After my workout, I have a shake with about 1/2 cup of oats mixed in. An hour later I eat 4 pieces of Ezekiel bread. On non-training days, I eat around 30 carbs total, mostly from vegetables, beans, and nuts.
I'm seeing nice gains with low carbs and calories so I would think that if you were on a bulking diet, you could put on some serious size if you follow the program.