A new one is mandatory if you break the one already on there while spreading the rear dropouts. But short of that- no a new bridge isnt necessary.
Perhaps call around to a shop or builder(there are a handful near you) and ask them to spread the rear if you are unsure about doing it well on your own. They can then realign the dropouts and check the derailleur hanger while they have the frame since those things take only minutes to correct if needed.