>Will there be a certification exam for VFP 8? If so, should I wait for that exam, or is it still worthwhile to pursue the VFP 6 exams?

There will not be any new certification exams for VFP because there is such a low demand and the effort and cost cannot be justified. The VFP 6 exams should work fine since they include core usage of VFP which hasn't changed such as data, programming, OOP, tools, etc.