What happens if I exile an opponent's Uro, Titan of Nature's Wrath with my Hostage Taker, then cast the Uro? Will it be sacrificed and go into my graveyard, such that I use the escape ability?
If a card would go to any players hand, graveyard, or library other than its owner it instead goes to its owners respective zone. So if you cast Uro in this manner it will enter the battlefield, you will draw a card, gain 3 life, have the option to play a land, and then it will be sacrificed and put into your opponent's graveyard.
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules