Can {Gaea's Herald} be countered? Sorry if this is a dumb question, I'm just really not sure.
You can counter it. Once it's on the battlefield the effect will hold.
112.3d (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=112.3d): Static abilities are written as statements. They're simply true. Static abilities create continuous effects which are active while the permanent with the ability is on the battlefield and has the ability, or while the object with the ability is in the appropriate zone. See rule 604, "Handling Static Abilities."
This appropriate zone is defined in another set of rules, one of which mentions countering:
112.6f (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=112.6f): An object's ability that states it can't be countered or can't be countered by spells and abilities functions on the stack.
However: {gaea's herald} doesn't state IT cannot be countered, but that creature spells cannot be countered. So, its ability functions only when the herald is on the battlefield.
Which leads to the short answer: yes, {gaea's herald} can be countered.
For reference: {surrak dragonclaw} cannot. (Note the two seperate lines)