...maybe. The features at union don't really even start to form until a min. 250, and even then only the top hole. Maybe if it were Sept. and there was really
nothing else to run, but there is plenty of other water right now that would be more worth your time than Union at 300. Also, Union is dirty water and horrible scenery, so it doesn't even have a low-water float trip allure. I personally would only go if I knew the holes were rockin'.
But Ras is right...you can float it down to about 100 and I guess that could be fun.