As I understand it, facts in evolutionary biology are such as these: all living things have a common universal ancestor, all verterbrates are (relatively closely) related and things like that.
Maybe you should make a distinction between observation and inference. We can observe that bats and humans and whales all have very similar bone structure in their "hands". We can infer from that observation that they all have a common ancestor. I'd be cautious about calling the inference a fact, no matter how confident we are in its accuracy.