Paint a rusty hinge without sanding?
Depends on if you want it to look good or not.  If you don't care just go to local big box and grab a can of spray paint - I use the rustoleum auto body primer for any metals.  Then I go over it will whatever type of spray paint - usually a bronze or satin finish.  If you don't sand it you will have rust bubbles in your paint and unless you use an obnoxious amount of paint, you will have pitting and bursted bubbles, given that these plates are hitting each other constantly.  

It is really all about the look you want.  I have seen people keep rust for an antique look and just a light spray of metal paint.  And then I have seen people make them look like new which involves sanding and painting as I prescribed above.