Well the only thing that can be apparent to anyone studying the symbol of the unicorn is how undefined it is, from this to that folk tale it changes its meaning based on what the folks using it imagined it to mean. For plenty of time it was seen as an allegory of christ and that story about the virgin was seen as an allegory of Christ entering the womb of virgin Mary so as to be born in human form. I am sure there are also alchemical allegories (if I had to guess at their meaning they probably have to do with something like the unity of spirit and matter, or will and form etc etc)... Though as it is with any symbol there are some basic ideas and associations that are universal and that act as a seed into which a thousand offshoots can branch. If you want you can definitely find a more base sexual offshoot among them. That is not how it is used in the book however.
The article you presented does not seem to be very good, nor is it well researched or balanced. But hey, populist notions sell - sex and all that spicy stuff. For what it matters - how one uses a symbol shows much about his character. A symbol is in many ways like a mirror, a representation of your own soul fixed upon a certain idea.
And by "spell" you mean what?