CRIMINAL IMPLICATIONS: Is it possible for a person to be imprisoned for keeping or harboring a vicious animal?

Yes it is, and there have been numerous instances where people have been criminally convicted for knowingly owning dangerous animals. 

In some California cases, animal owners have been found guilty of murder when an animal's attack killed another person. Sentences have ranged from severe fines to significant jail time.  I once represented a dog bite victim who sustained a dog bite from a dog owned by a person who was maintaining a dog fighting ring in his back yard in a local San Diego area neighborhood. Needless to say, the owner faced both criminal and civil penalties.