I don't like pewdiepie at all, but he always struck me as someone who would do exactly that, recommend something he hadn't vetted due to laziness and taking the easy way out. That doesn't make it ok, but I definitely think it is 50/50 that he knew about the content vs he didn't and still promoted the channel.
Shitty either way though, promoting something like that knowingly or through ignorance.
Since no one replied to this, I'm just going to point out that Felix Kjellberg does not deserve the benefit of the doubt. Ignorance is a valid excuse once, no more. You don't know better, then people tell you you don't know better, and then you do.
Felix's already apologized for normalizing Nazis, which should tell you he isn't ignorant anymore. The apology was total bullshit anyway because he was laughing about it elsewhere at the same time, and he's exchanging tweets and such with a bunch of white supremacists, which would be very odd things for an ignorant person to be doing.
And at times, he doesn't even bother to pretend. People mention the video where he got caught saying the N-word. If you listen to it, it's followed by a conversation over voice chat about how it doesn't really matter because the fans won't care, and the only people who will take him to task over his racism aren't going to watch his videos anyway.