|African rock python. Taken from http://largestfastestsmartest.co.uk/wp-content/uploads/2012/04/juvenile_african_rock_python__koedoesdraai.jpg|
A quick look on Wikipedia will tell you that "Pelvic spurs are the externally visible portion of the vestigial remnants of legs found on each side of the vent in primitive snakes . . ." This is where it would not be wise to consult the Wiki world. Although this was cited from Pough et. al's 1992 book of Herpetology, a quick search of other sources will say that pelvic spurs have absolutely nothing to do with long-gone legs. Although limb remnants can be seen in snake skeletons, the pelvic spurs have no connection to the skeletal structure. Possibly, pelvic spurs are simply modified scales.
Unfortunately, I cannot find a single reference to pelvic spurs in my own herpetology textbook (Herpetology, 3rd by Vitt and Caldwell). I have not even found a reference to whether female snakes have pelvic spurs, whether or not they use them. A firsthand look at the UMM ball python would be unhelpful to answer this question because he is male.
In sum, pelvic spurs are NOT vestigial legs but ARE a plus with the lady snakes.