Uncured bacon does not contain synthetic nitrates (that's what "uncured" means).
Nitrates aren't really that big an issue, anyway - studies showing negative effects involve isolated and unrealistic quantities of nitrates. Heck, I remember Robb Wolf mentioned in one of his podcasts that there's more nitrates in a spinach salad than 300 hotdogs.
I'm more concerned with the quality of the pork than whether or not it contains nitrates. Usually, uncured bacon is going to be higher quality, because it's catered to a higher-end clientele that is more health conscious than the minions shopping at Walmart. If you're getting your bacon at a farm shop or butcher, I wouldn't worry about it - the quality of the pork is most likely fine.