I can only speak for BG's because that's all I use, but we have used them to swim with!
I just took the insert out and put the outside part on. It was perfect!
I read about it and what I found was that really swim diapers only catch the poop, but the pee sort of goes in the pool. So using a CD in the pool was the same as a swim diaper.
I was cautioned that the chlorine could fade the diaper so I set one aside to use for swimming, but it didn't fade at all.
I did get a pack of 25 swim diapers at a garage sale for $1 so I'll use those this summer, but just FYI you can use them for swimming :) Just take the insert out, or else it's H-E-A-V-Y! My dad make that mistake, lol.