It depends what feed they use... the media tribune for instance has 8 direct feeds to it. One of those is similar to the one they'd feed to other broadcasters but without any of the logos and scores etc. One is a static overhead etc. The one on the big screen is more than likely the same as the broadcast images but I noted the other day they removed the time and score from the Durban one towards the end of the game.
It would not be the exact same feed as the one to SABC or Supersport though as that one is delayed by about 4 seconds or so and it would be disconcerting watching that live on the big screen (the delay, by my understanding, is caused by those images being "uploaded" to Nasrec, packaged and then transmitted). We'd often have both feeds on at the same time on different TVs in the media centre and the time delays were significant.