The only comparison between Foreign Wives and Zebulun is that they both have a one-time, upon-entering-battle check for a specific condition. Whether or not Zebulun's ignore updates with hand size has no relation to any ruling on Foreign Wives.
Zebulun checks upon entering battle whether all your heroes are Genesis and, if so, it activates his ignore. The ignore (an ongoing ability) is then continuously calculated based on the number of cards in your hand. If you play a non-Genesis hero after Zebulun is already in battle it won't deactivate his ignore, and if you had one in play when he entered and get rid of it later it won't activate his ignore.
