I think spokespeople in general have pros and cons.
Yes, they attach a famous face to a particular cause or movement or whatever that can garner publicity and help with moving things forward in a faster manner, but they can also bring negative publicity if there is any fall from the public grace. (Not saying Zimmern is going to suddenly turn into Justin Bieber or Lindsay Lohan, but you get my drift.)
Personally, I like Mr. Zimmern and his show(s). I find his take on food to be interesting and his adventurous eating to be a good example of pushing yourself beyond your culinary comfort zone to find new edible treasures. Like many "foodies" he is a big proponent of farm-to-table and of not wasting anything from an animal you butcher.
My wife, however, hates him. Won't watch his shows and either leaves the room or changes the channel when he comes on. For her, he would be more like an anti-spokesperson. (Now, if George Clooney was a permie spox, that would be another matter entirely.

)
Interesting idea though.