As far as I'm concerned: do, if you want to. I'll be excited to help in any way I can.
If you're going to use my exact words, you need my permission. Get with me and tell me which sections of my text you'd like to use. In general I don't have any reservations about this, so probably I'll just say yes and away you go. If you want to use, like, whole chapters, or my character playbooks, or really extensive pieces, that'll mean licensing them from me.
Better if you use your own words! Then you don't need my permission at all. I hope you'll give me and Apocalypse World a mention on your credits or notes page; do that and I'm happy.
This applies to hacks with wholly original content only. John's and my Knife & Candle hack, for instance -- we'll need to get with Echo Bazaar's owners if we want to really make anything of it. If you decide to make a Star Wars hack, well, that'd mean licensing Star Wars. Good luck with that!