That's really a no no...
If you want pictures in the park you can book that through Disney Photography Services. A portrait session will probably run you about $500 or more with only a small portfolio of proofs (maybe about 20 4X6) pictures. All enlargements would have to be purchased seperately and a photo CD goes for about $1,000.
If you decide on DPS, ask for Mike Strickland. He has been with Disney for over 20 years and takes awesome pics. Here are some from our castle shoot.
http://www.disneyeventphotography.com/