Yeah that's how it is. For Ze/Zir Zir takes the position of him and his. Which is why I only included the two forms.
"I borrowed his car" becomes "I borrowed zir car".
"I asked him for $20" becomes "I asked zir for $20".
In the case of Xe/Xem/Xyr it goes
"I borrowed xyr car" and "I asked xem for $20" respectively.