No, it isn't. I heard about it from my nephew when he was in boot camp. Not an urban legend at all.
A friend of mine just enlisted in the Army and will be leaving just after the new year. His recruiter just told us that he was under the impression that stress cards were still used at the "co-ed bootcamps" but not at all of them. I have no idea which Army bootcamps are co-ed or exactly what he meant by the term.