DreamHost fully supports IMAP 'IDLE' - which provides push notification. Many devices including desktop e-mail programs, android native mail, blackberry, windows phone, etc, will get immediate notification when using Dreamhost IMAP. Apple decided not to support IMAP "IDLE" for IMAP accounts, so you will have to use fetch to get updates. This is the same no matter who your provider is.
Your work-around would be to use ActiveSync. You can install a program such as 'z-push' on your server to act as a man-in-the-middle to convert and ActiveSync connection to IMAP on the back end, thus allowing your iDevice to get the push notifications that way.