Hill orcs almost always appear in large groups. They frequently carry scimitars or orcish daggers, and wear orcish helms. The Orcish Town variant of Minetown features large numbers of named hill orcs, who can also be encountered elsewhere in the Gnomish Mines and the main branch, and they will often have looted items such as keys, candles and depleted wands in their inventory.
Hill orc numbers may be formidable and pose a problem for unprepared characters, but they are easy to defeat individually. Hill orcs usually mark one of the first instances where you will have to use crowd control strategies, such as drawing them into a corridor so that only one of them can attack you at a time. Be wary if any of them have scrolls or wands on hand.
Hill orcs make a decent source of food for a starting character, providing 200 nutrition; their corpses also make for good fodder for sacrifice if you can keep them close enough to an altar. While this applies to most monsters, orcish characters will especially appreciate them—they lack penalties for cannibalism and stand to gain a lot more from same-race sacrifice, including maximizing Luck and summoning peaceful demon lords and foocubi.
The Orctown altar in particular may be worth converting for orcish characters for this reason, especially after procuring the luckstone from Mines' End. Make sure to convert it (with an ordinary sacrifice) before sacrificing any orcs, as you will lose Luck if the altar is unaligned; still, losing Luck may be preferable to letting the corpse rot and wasting a chance to get one more foocubus.