[vintermann]

It can be. Being professional doesn't mean being good, it means doing something for money, and there is money at stake in some online blitz tournaments.

One important question is whether Niemann has cheated in tournaments with prizes or "only" in ladder-type games (he's only admitted to the latter as I understand)

[perihelions]

It's professional either way, since he used his Chess.com profile for his Twitch streaming.