Things differ somewhat from state to state, of course, and I am going on how things work in Georgia, but if Louisiana is similar: Neither the defendant nor the defense team is usually at the GJ session, and there is, I believe, no judge present. At a recent high-profile murder GJ session here, I believe the only persons who were in the room during the session were the grand jurors, the district attorney, and one witness, who was the lead investigator in the murder investigation.
There are a few situations, if I understand correctly, in which the defendant and/or defense team might be present, but they are not common, as I understand.
As to the defense being privy to new evidence as it develops: At this point, they are probably not privy to much at all. Discovery does not happen, I think, until after arraignment -- at least here in Georgia -- which happens some time after indictment. There may be some informal providing of certain information to the defense earlier -- to encourage a plea, for example -- but the bulk of the evidence would not be provided the defense at this point.
I'm no lawyer, so if someone is one and needs to correct any inaccuracies in my statements, please do jump in!
