I did a trip that included both Zimbabwe and Namibia. Not really any problems. I spent a little more than a week in Zim, then flew to Winhoek and met my next outfitter for a short week of plains game hunting. I really liked the combination. My Zim hunt was an elephant hunt, and the only animal I harvested on that part of the trip. The Nambia plains game was an entirely different agenda, with just some laid back plains game hunting, and seeing a different part of the world. A great way to relax and pull the trigger a bit after a long, tense week in the thick jess of Zimbabwe.
I treated them fundamentally as two separate trips, but booked the diversion to Namibia as a separate flight. No special issues.
Bill