Not from the data I collected they don’t. Not during events at least.
Every time I get a gnome in the vault, it’s from a vault key drop by a pet gnome.
I’m still baffled by the choice to let the legendary gnome drop far more likely than any of the other common gnomes. I’m drowning in a Cedric clone army, and still no Jewel Gnome in sight.
I brought this issue up very soon after Cedric got his super buff but nobody else backed me up. I guess due to very few had him mythic at the time. Hopefully now more people will speak up how ridiculous this is. The only reason for the super buff was to artificially inflate the average “value” of his loot table.