Oni works on his own pace like he wants, and really he doesn't own anything to anyone since he's not a company and just self-employed artist. I'm not gonna argue deserves he these money or not but you can casually get access to his game just for 1 buck a month, and his target goal (last time I checked) is per month is 500$.
Debatable on this point. The moment he turned this from a hobby-project to a crowd-funded one via patreon, he entered into a business model where he does owe, if not legally then at least morally, a certain measure of professionalism.
But, with that said, people can remove their pledges at any point if they are not satisfied with how it is used.
Far from me to say what someone should do with their money. A fool's money hardly stays with him for long.
Still, I reserve the right to think it is stupid to allow yourself to be so transparently fleeced and that it is cheap and downright dirty to misuse the trust given. This project has since long passed the point of "draggins its feet", and I have professionally seen a lot of people trying to pull this shit off.
tl;dr: Not illegal, still immoral. People are idiots. Dont get upset about stupid people or you will be mad all day.