From what I had gathered, you can log it as PIC or SIC, it all depends on what you agree on. You can log it as PIC since you are the one responsible for the safety of the flight, and he would log PIC since he is the sole manipulator of the controls. But should something, like a violation, and you log the hood time as PIC, it is you who gets investigated for the violation while the other guy was under the hood.

However if you log it as SIC, then you don't have that amount of responsibility. Plus, you can log it as SIC time, since flying under the hood requires two pilots, according to the FARs.

You have to agree to what it will be logged as, and you will be the sole authority of the flight while he is under the hood. It is very complicated and worded very poorly. It's one of those gray areas.