I'm not sure that is technically true. I think the most common problem with "ab work" is the misconception that hundred of reps of crunches and sit-ups will help.
Abs SHOW more with low body fat, but if the muscles are small and weak, then even with low body fat your abs will not look great.
If your bulking plan includes gaining some extra fat, continue to work your abs to build a strong core and you will be glad you did when you cut later on.
One of the best ways to work abs and core is heavy squats and heavy deadlifts, but if you want to add some isolation "ab" work, then it won't hurt.