Cooldown on tank junglers is always nice imo. That 0.5 seconds could mean live of death though. I understand where you are coming from and I think that putting points into Perseverance and Second Wind is a great idea. I just personally prefer the extra cd because as a Nasus main, cooldown means everything. Its all personal preference. Plus I also feel that buying Spirit Visage can make up for not having Second Wind and Warmog's Armor more than well covers the possible percentage health you could be gaining with Perseverance .

You could also do like a 4/26/0 mastery tree. I feel like 9/21/0 is a pretty standard tree for Volibear. I do not want to put all my points into the defensive tree. Cooldown reduction is always good because you can get your abilities faster. Putting points in this masteries will also work. This is just how I prefer to run him.