Wow, I had no idea about the slang of the word creature being a term for drinking. It turns out that the Irish were very heavy drinkers back then, according to the stereotype.
http://www.victoriana.com/Irish/Iris...alCartoons.htm
If "to creature" means to drink a lot, and the Irish were known to drink a lot, then the name "McCreachery" could have been a joke that meant "drinks so much that he's Irish".
If that's the case, then you are probably right that it is not really meant to be malicious (albeit still engaging in a stereotype).