Yeah, last time I was in hospital I was given Clexane injections to thin my blood - my main gastro doc (who I trust a great deal) told me there's an increased risk of DVT in UC patients. Apologies but I can't point you to any solid studies, as from what i've read the link is definitely there (http://www.cdc.gov/ncbddd/dvt/faq_dvt.htm#risk). (There's not much info but it confirms UC as a risk factor in the "Who is at Risk? bit.)
As regarding J-Pouch, have a look on the "Ostomies" forum on this very website - hopefully it should answer some of your questions. (I have no experience with the surgery procedure myself, so good luck!).