The gem drop rate from frogs was generally good, but the gem whores would always flock to the scarabs. The necrosis scarab/sebilite guardian/outzone platform camp was usually the place to exp if you cared about gems also. They had a high drop rate of all gems, and uncommonly dropped diamonds, blue diamonds, and black sapphires.
Leprous scarab loot table from 2000 - gem rate the same for sepsis as well:
http://replay.waybackmachine.org/200....shtml?id=5023
Comments regarding sepsis scarab from 2001, well before the nerf in Luclin/PoP:
http://replay.waybackmachine.org/200....shtml?id=5144