There does seem to be confusion among WPEngine customers from exhibit document. Whether they are in violation of the trademark or not is up to a judge to decide on. WPEngine have recently been doing a lot of changes on their website to clarify that they are not Wordpress. That does not automatically make them in violation, but it indicates that there were areas where they could have been more clear in their communication to customers.
I’m only talking about trademark law. I’m not arguing what’s morally right or wrong, that’s a subjective perspective. I’m not able to tell if Dreamhost and Bluehost are violating the trademark, but from what I know they are generic webhosting companies and not as easily confused with Wordpress. In my personal opinion having had a quick look at Dreamhosts page about hosting Wordpress. It seems quite obvious that they only host the Wordpress software, with prominent phrases like “optimized for WordPress” and “Recommended by WordPress.org”.