Your mindset seems to be that ripping is a viable method, and the only reason not to do it is because of morality. This I totally disagree with, if you Frankenstein a bunch of other sprites together it is sure to look like crap, and even if it doesn't then how close will it look to what you wanted? Unless you are trying to make a directly derivative work, it will not look like what you want. And if you want to make a directly derivative work, what's the point?
Anyway, if you can't draw a horse, and want to resort to ripping, then I don't think you have any business trying to get a professional job. It's not really as though you have to practice each different type of object before you can draw it, there is a fundamental skillset that will allow you to draw any 3D object, with reference for the specifics of course. A professional artist has built up these fundamentals so that he can draw whatever he needs to, and doesn't fall apart if asked to draw something he never has before, like a horse.
One more thing, your idea of a pixel purist differs from mine, and from all the opinions I've seen. It should be taken for granted that a pixel artist doesn't "rip" someones work and try to pass it off as their own. Ripping is something entirely apart from pixel art, because pixel art is creating art, ripping is not. A pixel purist to me has more to do with care put into the pixel techniques like AA, working with a limited palette, etc...