Are loops or rolls allowed in the "utility" category in any US-certified airplane or glider?
The main difference between Utility and Normal category in FAR 23 is spins and the limitation of bank angles in maneuvers.  Normal category is banks up to 60 deg and no spins.  Utility allows spins if certified for them, and banks up to 90 degrees.  


  Limited   acrobatic   operation includes: (1)  Spins  (if  approved  for  the  par-ticular type of airplane); and (2) Lazy eights, chandelles, and steep turns,  or  similar  maneuvers,  in  which  the  angle  of  bank  is  more  than  60  de-grees but not more than 90 degrees. 


I would imagine that a Hammerhead, being a chandelle taken to an extreme, would be allowable since done properly the wings don't go beyond 90 deg,  but loops and rolls are definitely out in Utility Category.