Web Albums HD for Picasa will let you view you Picasa Web Albums. From there it is possible to save individual photos to the camera roll in the Photos app if needed. Or vise versa.
If you are talking about the Picasa app on a computer, then you can not sync directly with a local album. iTunes only allows you to sync with folders {on Windows}, and the albums are not true folders. However you can choose to sync a local Picasa album to Google+, and that will show up in the Web Albums app.
I just tested this and it worked, though it did take the new album a while to show up. I'm pretty new to both these apps and Picasa, so that's about all the help I can give.