I have never ganked, I’m usually the one that is being ganked. I don’t particularly like being ganked, but the potential of being ganked, etc. is why I (and many with me) play the game. It’s the dangerous and unpredictable player element that makes EVE more then just a grindbox.
Streamsniping is a generally frowned upon activity, but CCP has indicated that they won’t be doing anything about that. That policy isn’t new for EVE Online.
(Death) threats out of character (and out of game) should be dealt with harshly! Others have stated that account banning resulted in another account just spewing harsher threats, just keep reporting, eventually they’ll run out of IPs… If you perceive the threats as serious, please report them to your local authorities.
If people do things you don’t like via Twitch, as a Streamer you have the option to ban them. If people send you threatening emails, you can just block those accounts. If they do it via chat or ingame mail, just screenshot it, document the accounts linked to that char and report it to CCP. Just reporting it once and expecting CCP to fix everything for you indicates that you have a serious disconnect with reality! These things take time and effort. Now… That is for RL threats, for in game, in character threats… This is EVE!
People systematically sabotaging/killing your mining fleets or PVE fleets, this is EVE PVP. Systematically killing your mining fleet means less product on the market, more demand for replacement ships, thus more demand and thus isk for someone. Is that the ganker him/her self? Of is that ganker hired by someone? Or is that ganker living on salty tears instead of isk? It is all possible and allowed in EVE! It also allows me to revisit those gankers from 10 years ago whenever I choose too… 
CCP has spoken out on griefing, but that was in my recollection regarding new player griefing, nothing more, nothing less. Heck, some people even shower a new player with millions of isk when they kill a ship and then realize it’s a new player. They often even apologize, it’s not everyone that does this, but it happens more often then I thought possible!
That said, HateLesS is generally a nice guy, very helpful on stream, always willing to listen and explain things. So people getting a kick out of harassing people like that, I call bullies. I don’t like bullies. But what you don’t do is giving them satisfaction! In this case that’s exactly what HateLesS is giving them. He’s annoyed, he’s quit streaming EVE, he’s made a YT ‘I rage quit streaming EVE’ video. Expecting them to stop now is like asking the hyena “You ate my arm, isn’t that enough!?”.
By now the griefers should know all his character names, the locations and content he likes to farm and how he does it. I suspect that they won’t stop until HateLesS quits the game, and that is a shame! But we knew going into EVE that people could do this, that people are allowed to do stuff in EVE your not allowed to do in other games. Isn’t that what drew us to EVE in the first place? The stories about massive spy, steal, and sabotage jobs.
HateLesS has had this issue in the past, but it seems like he’s had more of this since he moved and joined a NullSec corp. I’m not sure if that’s true (maybe someone can enlighten me), because I’ve not been watching much (either the time slots were horrible for me or the NullSec corp content wasn’t interesting to me). I’m pretty sure that the type of content and how you stream it are going to influence the kind of people you attract (both good and bad).