So obviously my question is about the Moisture Farmer. If he protects a Tatooine objective can I then protect him with a Guardian so he doesn't die?

Yes.

In this example, only if it's a single damage, as that's the limit of how much MF can take with his protect in the first place.

Even better... protect him with a wookiee. The objective goes undamaged, the farmer lives, AND the wookiee's extra icons switch on! XD