Showtime, The Movie Channel, and the Starz/Encore networks tend to respect OAR and will air movies that way when a proper transfer is available (for example if there aren't any 2.35:1 HD transfers of a movie available for a movie they are airing they will have to resort to using the 16:9 version instead).
HBO and Cinemax are the opposite. They want everything in 16:9, however some movie studios/filmakers have refused to allow them to air their material chopped down to 16:9 so in those instances they will relent and air the OAR version. I remember reading an article a while back about the director of one of the Oceans 11/12/13 movies having to go almost all the way up to the president of the station before he was able to get HBO to relent and show his movie in it's proper OAR.
Like the others said though, there are no true 2.35:1 sources at this time (at least not on Blu-Ray or pay TV). All of them are 16:9 sources letterboxed down and you will have to use a scaler and usually an anamorphic lens in order to zoom in the material and show it full sized. I'm assuming the installer making your theater room will know all this and get you set up properly though.
I'm hoping when the Blu-Ray folks come out with Blu-Ray 2.0 or whatever they call it when they move to 4K/8K they put in a system to allow anamorphic encoding for wider formats, or maybe just remove the restriction altogether and just let the movies be stored on the disc at whatever width they need to be to have the proper height. For example have 16:9 material stored as 3840x2160, 1.85:1 stored as 3996x2160, 2.35:1 stored as 5076x2160 etc. And then just have the players downscale/letterbox the material if they need to show it on a 16:9 screen.