I am not entirely sure how, but I managed to get both aspect of the fox and hawk on at the same time. I have been close before, doing it by accident with hawk and cheetah or pack, but since I didn't quite understand how it works I haven't gotten it just right.
But today, by complete accident I managed to get hawk and fox on at the same time.
Hawk seems to be passive, and I can change fox to cheetah/pack/wild without losing it. I am not entirely sure how I did it, but I am positive it has something to do with camo and buffing changing aspects within/without of it. Try it for yourselves and see if you can't ascend to the next level of hunterdom, odds are you have already done it and didn't realize it.
All I did was have fox active, then turn on camo and as quick as I could turn on hawk.. and they both stuck.