Leg hair for eyebrow transplantation
My experience has been that leg hair does not work too well for transplantation purposes as it is difficult to extract via FUE procedure. If you don't have the right texture on your scalp which is similar to the eyebrows you can use leg hair as a last resort however your results would most likely not be so great.
Leg hair don't work well
From past experience of seeing unhappy patients (from other doctors) who had eyebrow or hair transplant with donor hair taken from legs or other parts of the body, I would personally not recommend it to any of my family or friends (which means any of my patients).
Maybe I am biased because I've never met happy patients (since they are seeing me for a corrective surgery).
Finally, if you are a woman and you want to harvest hairs from your legs, you WILL have permanent scarring in the form of tiny white dots on your leg from where the hair was taken.
Eye brow transplant
Usually with eyebrow transplant the hair that is harvested needs to be closest in texture and quality to the eyebrow area. Most doctors prefer scalp hair, but if your scalp hair does not have the same texture, you would need to be seen from close up to determine if your body hair is an option for your eyebrow. Keep in mind that BHT is done by many doctors usually as a last resort. The reason being that there is no evidence to suggest that body hair is long lasting and you may lose it in a few years.