I have done the Grand Gathering Safari Celebration at Tusker House twice.
The buffet was very similar to what is normally served at Tusker House and Boma.
A word of caution... when we did this the first time, a few years ago in July, we loved it. So, this past December we did it again. Big mistake. It was a rip-off... as it was already nearly dark by the time the safari took place, the animals had almost all been taken in, and the driver sped through the whole thing fast than a normal safari (we had already been on it earlier in the day, so we had something fresh in our mind to compare it to). Our CM tour guide admitted that Disney encourages them to go more quickly through the safari in this scenario since there isn't really anything to see.
We basically paid $60 a person for a meal at Tusker House. Not worth it. (Don't get me wrong... we love Tusker House... but it is not worth that price.)
So, please consider when you are planning to do this. If it will still be light out when the safari is taking place, you likely will have an experience closer to what we had a few years ago in July. But if it will be getting dark... I'd say skip it and try one of the other GG events, such as the IllumiNations one.