If the hospital will allow it - then go for it.
However from experience working in anaesthetics for c/s i know that it is usually not an option for a number of reasons.

* the theatres arent that big and already have average 6-7 + mum and partner in there already to perform the procedure.
* There is more often than not time for a nurse to take photos for you(i always made a point of doing this for the births i attended)
* it adds another infection control issue having another person not scrubbed in
* There is a lot of communication between anaesthetics, the surgeons, ob, midwife, scout and scrub nurses and another person speaking in the middle of a procedure could cause choas and distract the staff from doing what they are trained to do.
* recovery is not a place for another person (advocate or not) to be standing about, it is usually an open room with other patients, often indecent in their clothing due to close observations and i think it would be inappropriate to have someone standing there just so they could tell the NUrse (which is not always one on one) what to do.

But like i said, i am all for it if the hospital you are going to allows it to happen.