Is scaevola a perennial or annual? Garrett calls it a perennial in his Plants for Texas, while a major nursery in Dallas identifies it as annual. Which is it??? If it is an annual, can I pot it and greenhouse it for the winter?

It's probably a "tender perennial" meaning that if the winter is mild and the plants are mulched they will probably not die. Nurseries may tag it as an annual so if it doesn't make it through the winter, they won't have an angry customer on their hands....IMO.