I just read this page and it says that Bigfoot can't do any romatic actions at all, no matter what. But if you have hacked items (for example the Insiminater and Lizz Love's Water Bed) it is certainly easy to have Bigfoot become a father the old fashioned way. I have a sim who's currently married to Bigfoot and they have triplet girls. They all have red hair and green eyes, which they all got from Bigfoot. I'm not sure which skin color is genetic for him as all 3 girls have a different skin color and their mother is a mixed race baby as well.
Their daughters are teenagers now and Bigfoot and his wife still have an active relationshipwithout using any cheats and using a regular bed.