Well, I've been with the same host for over 6 years and never one had that issue, I know they are really good about notifying customers if there is a problem with any server.
My old forum was DDoS'ed a few times. Host would acknowledge it and recommend things to help, like using cloudflare, etc. Why would they act like it didn't happen?
Also if you were a constant target of DDoS'ing, I would assume they'd terminate your account eventually because you are a liability and having you around is hurting their business operations.
Moral of the story, run your forum fairly and try to be on good terms with everyone. Don't go out there making enemies and pissing people off.
Having had a few over the years for various reasons (both me personally and my professional clients), the sooner that I and the hosting company have a conversation, the better.
Fortunately, CloudFlare soaks most of the damage up these days.
My forum was once DDoSed so badly that a protection screen had to be implemented before accessing the board. The forum software owner implemented this, so he ensured my board and his network were protected.