Here is an explanation of aurat taken from wikipedia
https://en.wikipedia.org/wiki/Intimate_parts_in_Islam
They don't have to wear hijab, but they should cover their aurat. However, the hijab is one of the standard forms of clothing used to cover the aurat.
Specifically, any religion that has a vegan diet, for reference you could visit this site, http://www.chewfo.com/philosophical-reasons-for-food-choices/religious-dietary-restrictions/