Qualification: I am a master parachute rigger and I taught sport parachuting for 10 years.
The back door of a 747 is actually in a pretty good position - the tail is above the door and the fuselage is narrowing at that point so it's not a complete side exit.
A freefall jumper will drop out of the aircraft's wake in under a second so that's not really an issue. If we pick a theoretical worst-case where a jumper goes straight through a huge vortex they might get flipped over. Remember that a human does not have large surfaces like wings to interact with. Any jumper that can't recover from that won't be doing freefall jumps anyway. Seriously, this is in the Jump #1 stability lesson, and if you haven't got it sorted by jump #6 any reputable school will send you home.
Exit speed is a consideration - sport gear is meant for < 200km/h. If we are going out at 747 cruise speeds I would tighten everything right up1, wrap some tape around the riser covers2 and tuck the pilot chute handle completely into the pouch. Maybe also tack the closing flap cover down. Yes guys, it will still open if you sew it to the proper flap. If the plane is at approach speeds with flaps and gear down then you're fine - not much different than a King Air.
So in conclusion, yes, you can jump out of a 747. Rent one and you will have every jumper in the state lining up for tickets.
To reply to the comment of the pilot chute going over the tail, that happened at our place too (and to me once, but mine went under the tail). It's got nothing to do with turbulence - the pilot chute got pulled mostly out of the pouch, most likely snagging something, and the air picked it up from there. Our guy actually hit the tail. He had nasty bruises and needed a few lines changed, the pilot needed new underwear, and the Cessna needed a bunch of rivets and sheet metal work. When it happened to me I had a surprise deployment at 9,500 feet and a longer than usual ride down.
1 to the point where you will need my tools to close it.
2 it will break away after opening, and won't be more than an annoyance if it doesn't