But, do they swear to protect us should the call go out? If so, I don't see anything different at all. If they are killing terrorist, why would I care if it were the Army or the National Guard? They are still our military.
The actual oaths are here on this form, on page 3. Section 16 and 17 apply only to the National Guard, while Section 15 applies to everyone else who is joining the federal military (i.e. not joining the National Guard). (There are other oaths for soldiers joining a state defense force, but I don't want to get too technical here.)