Official WDW Hotels means that they are physically located within the boundaries of the Walt Disney World resort. The 7 Downtown Disney Area Hotels (on Hotel Plaza Blvd) along with the Swan & Dolphin are all "official" hotels. The reason that they can say you are guaranteed entry into the parks is that you are staying ON-PROPERTY and using Disney transportation. All 7 of the DTD area hotels share bus routes (though if I recall correctly, there are 2 different buses that service those hotels...something like 3 on one run and 4 on the other). Just like the Swan & Dolphin are on the routes of Disney buses. By being Disney transportation, you will be taken to your destination and able to enter the parks...vs. those guests who are staying OFF-SITE and then either driving on-site to the parks (or using those off-site hotel buses) that will be stopped at the toll plaza for each park and not allowed entry if the park is considered to have reached its' daily capacity.
As a pp said, if it were the Hilton that you were staying at, you'd also be eligible for the Extra Magic Hours, but that's the only DTD hotel that qualifies for that. None of these hotels (including the Swan & Dolphin) are eligible for the Dining Plan.