Hi Ken,
If you are doing the 5x5 SL program on 1/3/5 its recommended not to overdo cardio on the offdays especially swimming. because it can effect your arm exercises also (benching) if you do it too much.
As for the style of swimming, I am probably on the same boat as you. I swam everyday when I was a kid, now 8 years later I just started again. And it is tuff starting. As you read my previous post, I am having problem; however everyday I see myself improving like lifting

And the form wise, I just do what I recall when I was a kid and watches other people in the pool. Once in a while these two guys on the university come swimming so I just try to learn from them. I haven't done any reserach online for the correct form, because I believe i have it down. And also trial and error works pretty good with swimming. The speed, breathing, and power I can adjust and find the "right" style to train with.
However, I do not do the 5x5 SL program exactly as it is. I have a different kind of routine, therefore; swimming is one of the critical part. So I don't know how swimming will affect you if your in the 5x5 SL.