Direct ab training can help with strength, injury prevention, and obviously muscle. Totally neglecting them is like totally neglecting rear delts.
You don't necessarily have to do a ton of ab work, but some kind of flexion (a crunch variation) and some kind of anti-rotation or anti-flexion (Pallof press or plank variation) movement would be a basic start.
I just took a look at that. Seems old school (I mean that in a 100% positive way) and reminiscent of what some bodybuilders in the '70s would do. Guys like Serge Nubret, Zane, and Franco would often do high volume ab sessions, doing crunches for time, etc. Can't say it didn't work for them.
Alternating an ab move with a cardio-ish move, is also discussed in this article for "spot reducing" the abs:
So, very cool stuff, man. Glad to see it's working for you.
Yes, I think training the muscles responsible for a 6-pack will help with a 6-pack. In addition to a dialed-in nutrition plan, of course.