No, the tri shorts don't cause too much extra drag on the swim. They're bike shorts, so they're really tight anyway. I have found that I need to get a tighter tri top than I would normally wear (and I mean skin tight). When wet, that puppy will hold some water, so the tighter the better (and once in the water, it stretches out and then it's not too tight for the rest of the tri- and it's not like anyone is checking out MY bod in a tri, so I don't worry about it if my rolls are more prominent than normal on race day anyway). Sorry, that was a mouthful.
Short answer: no they won't cause excessive drag, and yes they'll work for non wetsuit swims.