I don´t think there is a problem if you defer at hks and then apply to hbs. I have friends that defered one year at more than one school in order to apply to other programs they found more attractive. Most schools will ask you to put down an other deposit if you want to defer. You have to be willing to lose that money. But other than that there should be no consequences.
Also, I think that when you apply to hbs they ask you if are a student at hks or are applying. Don´t lie about that. But i wouldn´t tell people at hks that you are defering only to try to pursue an other program. You would probably be denied your deferal.
