Photo hosting site Flickr is meant to be a place to share and organize your photos. As a way of advertizing, Flickr boasts hosting more than 5 billion photos, but most of the users would probably comment on the general quality of the photos posted there instead of how many there are.
As a potential marketing instrument, Flickr is probably not one of the first choices for Hilton, but it could add an "artistic" edge to the company's image. Pretty pictures are always a pleasure to look at - and considering that hotels try to sell with their IMAGE and visualization, an official Flickr account probably wouldn't do any harm!
A quick search reveals that the tag "Hilton hotels" brings up about 2500 photos - but most of these 2500 are all from the same user, who probably isn't affiliated with the hotel itself.