Devoid of the context of D&D, I might have guessed that a rutterkin is either the object or the outcome of hillbilly love. It seems highly unlikely, however, that Gygax was inspired to name 2nd level assassins after a viewing of "Deliverance." Still, I suspect that rutterkin is derived from literature; probably some murderous antagonist by some Appendix N author.
However, one of the only sources Google could dredge up that was not some demon from Latter Day D&D was this bit from Wikipedia: Rutterkin was the name of the cat/familiar that the witches of Belvoir used to kill the Earl of So-and-So in Merry old England back in the 16th or 17th century. While this is applicable in some regards--the cat was an agent of death--I'm still guessing EGG was not inspired by an ensorceled cat.
And while Webster was no help on this one--neither the online version nor my hefty New Universal Unabridged from 1979--The Free Dictionary came up with "an old crafty fox or beguiler." And that, I fear, might be it.
Also, there was an episode of an old, British Robin Hood series from the 80s (not the current British Robin Hood series) titled Rutterkin.
And another aside: the star of this series was a young man named Jason Connery, the son of James Freakin' Bond!