No (at least in my experiences). Every movie I've worked on has had its trailer done somewhere else. It's true that there are facilities that specialize in trailers, and that's all they do. Often times they will not consult with the sound team actually working on the film. They will, however, request specific clips like dialog takes from dailies or certain "set piece" sound design that is critical to the story, ie. a creature vocalization, a signature sound, etc. But mostly, the sound design is up to them.
Here in NZ we (myself & dialogue editor) tend to cut & attend the mix of the trailers of films that we do. The most important aspect of this, is to insist the trailer editor cuts picture referencing the original film in reels, so that we can conform the 5.1 mix stems..
If you do not get involved & pre-empt the problem, they will cut from a joined-up version which means you have to manually conform elements from mix stems... Of course each trailer has to be considered in its own right, and we receive an OMF/AAF of what the editor has done with sound - sometimes the dialogue editor goes back to original material from predubs or production sound, but having the 5.1 mix stems conformed is a good starting point from my point of view!
Having worked on a number of trailers for indie films, I can also confirm that the answer is no (in the US). In my/our defense, you'd often be surprised (or not) at the elements that we're provided to work from - audio from ripped DVD screeners rather than the final stems, the proverbial slammed-beyond-all-hope music from the stock library site, raw dialogue that is probably (hopefully!) ADR'd, etc... and all that on a shoestring budget with a tight turnaround.
That said, thankfully the trailer company that we work with is really great at editing their trailers... hopefully the sound has been able to match!
I have done some trailers for films and even more often have mixed trailers for theatrical release to promote television shows as well as television tie-ins using partially completed stems from feature films to make promos for behind the scene footage and sneak peaks,etc. I almost always get stems from the house that is mixing the actual film/programming.
I try to be as to true to the original as possible but as Glenn mentions above there will be times where there must be provisions made for "the sell." I have juiced up or thinned sounds to "up" the excitement of the cut. Often times the sounds that make the furrows and peaks that are necessary in the success of a long form story line must be tweaked a bit for a trailer or promo in order to make the specific cut flow and crest and grab the excitement of the viewer. It is a hard balance between wanting to design and mix something that will "sell" the audience but remain a true representation of the programming, especially as often the actual programming is not available in its entirety for me to view. I find you have to ask yourself if what you are adding is necessary to the successful communication of the message in the few minutes, 60, 30, 15, or 10 sec you have and if it still represents what could reasonably be within the sound palette of the actual programming.
No offense to trailer audio guys here but I find trailer sounds extremely bad. There's of course numerous reasons why, still, I never judge the audio for a film out of a trailer - which is slightly sad because a trailer is actually aimed to be better than the actual film, it is afterall a "sales pitch" to the general public(like Avatar - air bender).
But I remember the Transformers 2 movie trailer had lots of the original audio from the film already in it for the showing scenes - drooled all over it.
Often the video editor lays in their own temp SFX during their cut, and, depending on budget/time, these fx can end up in the final version. Depending how good the editor's sound is could determine the quality of the final sound..some editors are actually pretty good sound designers and sometimes not quite so much...It's usually quite easy to spot which trailers had a sound designer pass over them.
On occasion we will send them a piece of a pre-dub or stem but that's it. While trailers might not sound better than the film they are promoting they ALWAYS seem to sound bigger ... a lot bigger. WHOOSH! BOOM! WHOOSH! WHOOSH! BOOM! BANG! WHOOSH!!!