When the rules sat you can bring rosin for string instruments, does that mean bows are allowed? Now when I mean bow I mean a custom made one but with horse hair replacements. Then is horse hair a type of string they do allow?
By rule 3.a. horsehair has a string-like form and could be allowed, but they are also a part used in professional instruments which would prohibit their use. I suggest submitting an FAQ so you can possibly get an answer that you can reference if questioned at tournaments. As a supervisor, I would allow horsehair as it is almost a raw material with few refinements and in this way comparable to hide glue.
Some tips for working with horsehair. Lay out the hair and remove strands with sharp kinks. Thoroughly wet hair with water before installing and comb while installing; this will organize the hairs, and the hairs shorten as they dry. Tying hair with a good knot will help the hair hold consistent tension over time. Gilles Nehr on Youtube has good videos on the process, though he has odd 16 second interludes in each of his videos.
"One of the ways that I believe people express their appreciation to the rest of humanity is to make something wonderful and put it out there."