Adopting partial elements from the PB is better than none at all. You've got to start somewhere. If he's killing himself with chronic cardio, I'm quite sure that Primal exercise would lead to improved health. But even better, if he sees results, it might pique his interest in the rest of the PB.
Unfortunately, though, my experience is that fat loss is 90% diet, if not more. I was deeply in denial about this until I adopted the PB and experienced the results on my own hide.
Good luck with your husband! He's a lucky guy, because having a primal spouse is about as good as it gets. My wife's support has been foundational to my success.