some thoughts...
I haven't studied so specifically Crowley or some of the history of religion some folks here have, but I've studied "around" the subject of hero myths where the father was in animal form, and here are some of the things bumping around in my head about that:
First, in religions that incorporate some type of "animal-spirit guide," or whose pantheon includes animal or part-animal figures, it seems that some uncanny or "divine" attribute of the animal is what is, in fact, venerated, yes? Like for the Hindus, there was a belief that elephants were actually clouds come down to earth, do I remember that right? Something uncanny and enviable. The stealth, power and night-vision of cats... Etc. So for a person/hero who probably displays some kind of super-human attributes, formulating a part-animal parentage to explain that would make sense? There may not be a strict cause and effect here, but the two things -- the supernatural power of the hero, and the uncanny abilities of animals -- seem to fit together?
Second, it seems from what I have read, that in some contexts, Crowley disparaged knowledge in the sense of book learning, suggesting that it can be used to shield one from having to deal with wisdom that is "intuitive" or of supernatural origin. For example, considering "daath" in qabalah as false knowledge, and seeing it as a detour that delays one's true enlightenment. Some cults of animal wisdom, it seems, also suggest that humanity over-thinks, and that the way to enlightenment is to get in touch with one's animal nature. Actually, some branches of eco-feminism flirt with this idea -- that real wisdom comes from being more in touch with the natural world. Actually, I flirt with that a bit myself, although a Dominican education won't let me give up entirely my faith in the capability of the human mind. Recovering from this tangent, let me summerize that a hero's animal parentage might be seen to tie into the co-existence of animal nature/wisdom and human nature/wisdom in the hero.
Lust/Strength seems to celibrate that animal wisdom -- the wisdom of our desire, of what brings us pleasure, of listening to our "animal" nature. Where in Rider-Waite the pure young woman tames the wild beast, in Thoth, the wild nature of the woman allows her to work with the beast.
What do you think?