Yes, by all means supplement your Zone diet with fish oil. It eliminated my high BP and my doc took me off the 2 BP meds I used to take (which , BTW, didn’t even lower my BP out of the high range!). That was years ago and my BP is fantastic, averages 107/high 60's to low 70.
My biggest tip would be to focus on the hormonal control, the insulin lowering aspect. By doing so, you'll have the best possible results in the Zone, and the best weight loss results, too. If you haven't read a Zone book, I'd highly recommend Toxic Fat. After that, the ANTI-INFLAMATION ZONE, and if you want the best shot at learning all the details of the diet itself MASTERING THE ZONE (an excellent book to learn the details of the diet and how to tailor it to you needs, but not a source of current fish oil info , since it is one of the earlier books, written before much of the current fish oil research info was known).
Have fun with it!