Hoog was Zoltan Chivay's old friend and a member of the Scoia'tael operating in Temeria. Judging by his name, he could have been a member of the prominent Clan Hoog, current rulers of Mahakam.
In June 1270, he and Zoltan were supposed to meet in the Outskirts, but Hoog never showed up.
If Geralt kills the Scoia'tael during the Strangers in the Night: Not long after the two dwarves were supposed to meet, Geralt of Rivia asked Haren Brogg if he heard anything about Hoog. Brogg promised he would ask around but nothing ever came of it.