A person under the influence is always entirely responsible for their behavior, be that assaulting a stranger or driving a car into someone else. Being drunk doesn't remove the responsibility if you cause a crash, it makes it worse.

I do however think it make for a bad move if a taxi company has a open bar for cab drivers who is on the job. Its a design for disaster. The taxi company would have made a bad decision, and the drivers are still 100% responsible if they drive drunk. The one do not exclude the other.