Feraligatr gets Dragon Dance because it's based on a reptile. In fact, a lot of reptile pokémon learn dragon-type moves... that actually makes sense.
Now, Crawdaunt and Whiscash...
For Crawdaunt, this might be a clue:
I remember reading somewhere it was based on some japanese legend, but I'm not sure now...
I also found this:
http://www.petpeoplesplace.com/petstore/Japanese-Bronze-Green-Lacqur-KOGO-Lobster-Dragon-Meiji_150581489731.html
Japanese Bronze Green Lacqur KOGO Lobster Dragon Meiji
I amoffering what I believe to be a rare Japanese bronze with Gilded interior andGreen lacquered exterior KOGO having an embossed Dragon Lobster on the lid and Waves embossed around the outside, probably from the Meiji period
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For Whiscash, I found this:
http://historyofgeology.blogspot.com/2011/01/namazu-earthshaker.html
The dragon was a very old and powerful symbol imported from China and was in old times the main culprit of earthquakes, however during the 18th century, a giant Namazu gradually replaced the giant dragon in the popular imagination. This change from dragon to Namazu was minor, because dragons were also associated to water and rivers and so were closely related to the catfish in the popular imagination.
I believe this association made by the population was probably also influenced by the whiskers, as oriental dragons are usually despicted with whiskers...
ps: I'm not sure if I can post those links but it's for people to see the pages by themselves...