I was farming for the Dawnguard cache random encounters and was able to find Saliah and Lynoit, but not Hakar. I checked the corresponding quest (DLC1_WESC06) and its entries in the Story Manager in the CK, to see if there were any specific conditions I wasn't meeting. I found out that this particular encounter is classified both as a wilderness encounter (WEQuests) and a road encounter (WERoadQuests), and that can only be found in the hold of Whiterun from 0:00 to 8:00 AM.
After a while of still not being able to find it (I was also checking Frosfruit Inn in Rorikstead just in case, sinc