There are a few major differences with the real thing, which vastly change the psychological impact.
This seems to simulate life ON Mars, rather than travelling TO Mars. Big difference: on the journey there is far less to do than upon arrival on the red planet. Boredom is what gives rise to tensions, having (hopefully interesting) things to do is what keeps you happy.
The experiment lasts for 8 months, doesn't a (mostly boring) return trip take longer than that?
There is ALWAYS the option of bailing out halfway. Yes, sure, it's forbidden and so, but the option is there. The people in the dome know that. If they really want, if someone gets really sick with some life-threatening condition, they WILL be taken out. In the event of a real trip to Mars, that option just isn't there. There is no help around the corner, it is not simulated far away, it's really far away. Knowing that you are committed is a whole different thing than knowing you can make it stop, even if it is only in really extreme situations.
The simulation is a limited time, and a well known limited time. Participants can count down to the day they're released, and know when the torture wills top. That makes it much easier to deal with than the one-way trip as suggested by Mars One.
The above are all things that I know can not be practically or even ethically be done on Earth. It may make a huge difference, though, when a manned Mars mission would actually take place. How people really deal with the above is not sure. One of the main things may be how to deal with emergencies, especially the part where you know that you can never summon help - I mean just look at how people fall over one another about the idea of movie theatres jamming mobile phones, potentially blocking people from making emergency calls until they walk out of the theatre!