No. Urborg states that "Each land is a Swamp...". Since the card does not say "land card", it implies that it's ability only affects lands that are on the battlefield. Note that your fetchlands do also tap for black mana.
November 21, 2014 4:56 p.m.
7/18/2014: Urborg, Tomb of Yawgmoth isnt a Swamp while its not on the battlefield.
7/18/2014: Urborgs ability causes each land on the battlefield to have the land type Swamp....
So only affects lands that are on the battlefield.