The Blood Drinkers are a Besquith mercenary company.
From the Books: "'Oh, entropy,' Breetar replied. 'That’s a Besquith merc unit. I’ve heard of them. They don’t work or play well with others. They usually only take contracts where they’re allowed to kill and dismember their enemies. The people who’ve worked with them say their unit’s name isn’t symbolic; they usually do drink the blood of their enemies…and often while they’re still alive.'" - Asbaran Solutions, p. 76.