No they are not, at least not the stock openings. Wall openings are parked in the folder for Doors but they are really Generic Models (using the stock content).
They put them in separate categories because many firms don't include openings in door schedules. Then they confuse matters by dropping them in the Door folder. There is no Generic Model folder in the stock Content, there probably ought to be.
Unfortunately this leads to a bit of confusion with new users as they load a door but find that they are not listed among the doors. So they try loading them again (they ought to be in your template already by the way but they aren't in the stock templates). Still no door/opening family. I'm not certain how they get past this but I'm guessing that they ask someone, visit a forum or just start poking at the listed categories in the Project Browser. They may just start trying different tools, like Component instead of Doors which, surprise, offers them the opening families.
I wrote that I believe that there ought to be a better process to place components back in March 2007. That was when we had a Design Bar instead of the ribbon and we still don't have a more refined way to do it. I don't know that my old suggestion makes as much sense in the context of a ribbon. I just know that scrolling through long lists of families either in the Type Selector or the Project Browser seems a bit crude when the components are all categorized nicely already. Does it really make sense to have trees and shrubs in the same list with casework? I suppose it does if you are using plant families as part of the interior design? Revit MEP has a bit nicer work flow for each discipline and the electrical devices process is nicer still.
That's why I think this Opening is a Door, but isn't, is a Reviteristic