I might be in the minority here, but I did Safari at 6mo pregnant and thought it was fine. I've been on bumpier rides in my in car, lol! The biggest issue for me was just being on my feet all day. I so wanted to sit down on the curb at night to watch fireworks/parades, but was literally worried I wouldn't be able to get back up. Be sure to plan plenty of breaks.
I know a lot of people will immediately just tell you to ask your doctor. And while I would certainly recommend talking to them, I think it's worth remembering that drs are people too, with their own biases and opinions. Great example- I had different drs for each of my two pregnancies. The first acted surprised that I was worried about rides at all, and literally told me I could ride anything. He was of the "pregnant women have been riding and falling off horses for centuries, you won't do any worse than that" mentality. The second told me I shouldn't ride anything. Literally. Not even iaSW. Because, you know, I could slip and fall getting into the boat. Both pregnancies were normal, no complications, and my health was fine. Not saying either was right or wrong, but if you ask 10 drs the same question, you may get 10 different answers. Sometimes first hand knowledge from people who have actually experienced that very thing (i.e. this board) is more useful.