Can you substitute chicken broth for poultry gravy?

Yes, traditionally can be used (as can wine, depending on the recipe) to deglaze a pan (that is, dissolve stuck-on browned bits after panfrying meat). It's then reduced, and starch may be added to thicken it, and often times butter, herbs, or garlic or onions for additional flavor. It's a simple, common technique to make things like steak sauce.