As much as I love venison, it is a poor meat for sausage in itself. But like any other meat, if you mix pork/pork fat with it it's delicious. I'm not sure about the olive oil thing, I prefer good old pork fat! We are going to be butchering hogs in a couple weeks as we do every year. And I will be harvesting plenty of fat for cooking and sausage. The best fat for sausage is the stuff that is around the kidneys, it has the perfect texture/flavor for sausage. The kidneys eat well to, but you have to boil the piss out of them! Sorry! That's an old joke my Dad always tells...
The venison/pork and fat ratio can obviously be adjusted to taste, but you should have about 30% fat for good sausage. More pork certainly won't hurt the sausage.