At the risk of overreaching, since I don't know what your company does, is it possible that your boss is looking for a T-shirt HE would want to wear, rather than something that is necessarily a boost for the company, like when someone buys Christmas presents for other people that come from his/her own wish list? You might want to get a more specific idea of what he wants here.
Also, since this is going to eventually be sold to the employees, it might be a good idea to generate a range of different drawings to your coworkers and see if you can get a group favorite to give to your boss - he might accept a milder design if he thinks the employees like it.
Final thought: If you really want to balance a company logo with Harley-Davidson, and your company isn't really all that hard-core, you might want to trade the skull idea for something involving eagles, flames, and/or American flags. From a psychological standpoint, I think skulls are just too aggressive; eagles, flames & flags give you a little more flexibility with a logo-friendly design, and they still have a lot of edge. Heck, with your drawing talent, you could make roses look tough and dangerous, so I don't think you need to use anything as automatically confrontational as skulls and bones to get a Harley-Davidson look anyway. Good luck!