I figured they would pop when you kill those two mercenaries at the end, but no dice. How did you get the Grazer and Razoronn entries? Do you just have to kill them or is there a specific boss creature you have to kill like for the savrip?

They're basically the most powerful creature/droid on any planet. On Coruscant it's a huge Level 18 droid named "SD-0" that was 191,000 hitpoints and requires a sizeable group to kill. They unlock a codex entry and drop relatively good loot.

Grats on that. He looks like he was pretty tough.