After a lot of thought I came to the conclusion that "nihilist denialism" doesn't exist by itself and it is just "fall on deaf ears for hidden motives". My argument starts with the definition of nihilism: "rejection of principles". But this means that I could reject nihilism itself. Somehow a nihilist should deny nihilism itself, and this paradox looks unsolvable. My second argument is that something similar happens with the definition of God, that is undefinable by definition. Thirdly, and lastly, the only approach toward dismissing the belief of god is putting the burden of proof on those who claim its existence. Same happens with the nihilistic, because saying just "no" it's not enough.
This being my argument, it's clear that people like B.o.B. or Tila Tequila just run a business and use flat earth for marketing, similarly to Mark Sargent who clearly doesn't care about flat earth. For them it is pointless to look for sophisticated Philosophy.
On the other side, Science is indeed based on principles, and even though they led us to bridges, planes, computers, etc..., there's not a real way to claim they are absolute (actually, it'd be quite worrying to do so). Here is where the real flat earthers appear. I don't consider them skeptics, rather they speak a completely different language.
EDIT: I liked the link of Marcello Truzzi, he also seem to say that "negative skeptics" are often "cheating pseudo-skeptics". Apologize for my word salad.