At the same time, we have a completely different understanding of social media now than in 2011. 17 year old Hader in 2018 may not have tweeted that, not because he was a nicer person, he just would be more aware of long term repercussions.
In the end, it sounds like his teammates are all defending him and supporting him, so hopefully he's a good guy and that was just a bout of young ignorance and not a sign of who he truly is or what he truly thinks.
I know he's not on the level of a Josh Allen in football, but the agents are doing a piss poor job here. When they get hired a player, the first thing they should do is vet and scrub his entire social media platform. Not that every player has stuff as bad this, but there's usually something that can look bad when a player gets put in the public eye, and you know people will find it eventually.