No, it's not, and I'm not quite sure how to understand it. We do have expressions 'X monkey' where 'monkey' basically just means "person", or "person low down in the hierarchy; person we don't pay much attention to". So a caffeine monkey would be someone who uses caffeine and who - hmmm, who isn't very important? who doesn't have an important role in the organization? The rough idea is there, but it isn't clear what exactly is meant.