Does xanthan gum simulate yeast?

Xanthan gum doesn't function as yeast/leavener; it mimics the function of gluten in flour. XG turns the dough gummy and sticky, which permits the dough to trap gas bubbles from the yeast(or other leavener), which in turn allows the dough to rise. Imagine if you will a large piece of bubble gum. That's the texture of wheat flour dough, and with xg, that will also be the approximate texture of your GF dough. 

Now onto the matter of xanthan gum and fermentation. XG is made by fermentation, it does not itself ferment. Many things are made by fermentation. In the case of XG, sugars are digested by bacteria, and they excrete xanthan gum. Yummy, huh? Another example is vanilla. Vanilla flavor is created by the fermentation of vanilla bean pods. But it doesn't itself ferment or create fermentation in cookery. Many other things are created by fermentation. 

Rheology. There's a word for the game shows. Basically it means "the study of viscosity properties of substances." The next time you see a toddler playing with his booger, you can say he's conducting a rheology study.