Lots of folks post on here that there is no benefit to adding swimming to your workout routine. All of the Bowerman women swim daily. Does he have a different philosophy on swimming benefits?
Different strokes (lame pun intended) for different folks. Swimming seems to help the more injury-prone of the Bowerman Babes, like Colleen and Emily Infeld. If you have decent form, it can be a great cardio cross-training workout. You can get your heart rate up much faster than on the elliptical, spin bike or aqua jogging. I'd also think Gwen Jorgensen does some of it with her triathlon background.
But I've never seen Shelby, Courtney, Shalane, Amy, Kate, Marielle, or any of the others in that massive group post anything about a swimming regimen, so I'm guessing it's not a staple of Jerry's program.