No. The drain field needs the water from rain to flush the bacteria away. Also the ground in a drain field cannot support the weight of the deck without interfering with the function of the drain field.
I wouldn't. Every time you use it, you'd smell the nasty swampy graywater right underneath it. Plus, in order to keep it from sinking into your leach field, you'd need to drive PYLES (ha! Piles!) down to solid ground so they won't sink. Who knows how far that is, and who's to say that you won't hit something important in your leach field while driving the piles? And who's to say the excavating company will want to work right on top of your crap-water? If you can get someone to do it, it'll be expensive, and it won't be worth it because of the smell.