Although maybe there should be some research. If more pay automatically makes people go to the gym more often, maybe it would be ok...
I find vacations sometimes interesting and educational (see other societies, etc.), but not generally relaxing. To me, packing, flying places, and living in hotels is a bit stressful. To some extent, it actually makes me feel more busy, because it's one more thing, along with work, that gets in the way of me spending more time on the local stuff I'd like to spend more time on.
Or someone who wants to spend their holiday time with an old or terminally ill relative (which was my situation a few years back)?
Or what if someone just enjoys taking time off to do something entirely different but at home - say DIY or some other hobby? Why should they be penalised because their idea of a holiday is different?
Actually happiness research seems to indicate that spending money on experiences rather than stuff (for example) is a good idea. But I am not sure if it follows that it still works if you make people spend on experiences instead of stuff.
It doesn't sound like FullContact requires you to use the money in any particular way, they just won't give it to you unless you take a "vacation" (where vacation may be staying at home working on your hobby).