I remember hearing that Zanz stated that nymphs got a boosted fate egg chance, though i'm too lazy to hunt down a thread that says that.
Here's the total number of creatures in each element:
Aether: 5
Air: 6
Darkness: 7
Death: 8
Earth: 7
Entropy: 7
Fire: 6
Gravity: 8
Life: 7
Light: 6
Time: 8
Water: 8
Other: 0
Total: 83
1/83 = 1.2%
12/83 = 14.5%
24/83 = 28.9%
So nymphs and dragons make up more than a quarter of the creatures you can obtain from fate eggs. This is assuming you have just as much chance to get a nymph than any other creature.