Yes, you can make hair on rawhide. You actually have to remove the hair from the rawhide if thats how you want it. Not being able to seal the bow would be a real bummer! Plus the excess weight of the hair will detract from the performance of your bow. A few guys have done it over the years but I don't believe they were totally satisfied with it.
In the newest edition of PA Magazine(just coming out) there is an article about a guy adding bear hair to a bow by glueing one end of a bundle of strands over and over again covering the whole bow back.
I haven't read the article yet but doesn't look like something I'd like.