I think the idea is that the agent would negotiate the terms of the initial offer, i.e., this would happen before the tech worker joined the company. Certainly, once you're in, an agent is unlikely to be able to do anything for you. So the question is not whether it would get you fired but whether a prospective employer would negotiate with your agent. It depends on the circumstances, I'm sure, but in Silicon Valley, if you have skills that are in great demand, we just might be at a point where this could begin to work.