I honestly don't see anything wrong with them. I mean these kinds of nipples exist in real life. Everyone does not have just one kind of body type, variety is the spice of life and it is nice that the artist does something different than some of the other art.
Everyone's entitled to their own opinions, and the majority go "heeeugh" in reaction to those things going by the comments left on plenty of his other works.
If there weren't somebody out there that liked them, there wouldn't be an artist drawing them.