In theory, yes, you can. In practice, that's a pretty long, heavy blank, especially on a lathe of that size. If you round the blank between centers first, so it's reasonably balanced, you might get away with it. You'll need a really well made tenon to keep the wood in the chuck and turn safely. If you do try it, I'd suggest keeping the tailstock in place when possibly to reduce vibration and enhance safety.
Going from green wood to finished urn or large vase is a real challenge for me. If I wax the ends on a blank and let it sit, in 4 years, I may have a blank that hasn't cracked badly. If I rough turn the blank, it'll dry faster, but then in order to minimize cracking, I've got to turn a reasonably uniform wall thickness and I'm locked into a particular shape. I wish I could go down to the local lumber yard and buy a nice, dry 6X6 hardwood blank.
It's one of the more frustrating problems, for which there doesn't appear to be a good solution here in the arid west. You at least have plentiful hardwoods, a little humidity, and some chance of success.