It's funny to me how many people think blood craze is really bad. Which in PvP/Trash PvE were you want burst damage, yes it might be. But against any kind of boss encounter that is going to take more than 9 seconds to die... twin slashes is really good. My dungeon running bar setup has blood craze on it, and you just keep it up without clipping just like any other mmo with dots.
I'm not entirely sure what "Blood Craze" is but I'm going to assume it's a spell. If I am right in saying it is a spell does it specify anywhere in the spell description about it stacking ( if it says it stacks then yes you will get more health the more enemies it's on ) if it does not specify then you'r going to have to give it a Google or test it yourself. Or you could just wait for some one more knowledgeable on this topic then I am. That's all the help I could give I hope it helped.
I don't know if this has been answered already, but Blood Craze does not stack when applied to multiple enemies.
The way the ability behaves places a buff on yourself when the bleed effect is active. Each time you recast the ability, you refresh this self-buff. As long as the self-buff is present, you will receive a HoT.
You can not have multiple Blood Craze buffs on yourself, each time you use the ability, you just refresh the single self-buff, thus stacking the ability on multiple enemies will never give you multiple HoTs.