My personal opinion...No, I don't think veno's should have BP. As "beardragon" said, and I quote:
Venos don't need BP as they should not be getting hit much, they have many ways to kept themselves from being hit. Plus they have a skill that allows them to heal themselves up by switching MP and HP values and a self heal skill.
Metabolic Boost is a great plus for veno's. (Healing Skill)
And Soul Transfusion (Switches MP to HP)
That's more than enough. And charms being so cheap for HP and MP, that's already a huge advantage.
Just my opinion.