Can someone defend against a fault claim of divorce if one spouse is imprisoned?

It depends on the jurisdiction and the crime. For example, a person going to prison for three years for vehicular homicide while intoxicated may find it harder to prevent a divorce than a person going to jail for sixty days for a third offense of drunk driving.

Yes, in most states with fault grounds, confinement in prison is a fault that can lead to divorce. Each state specifies how long the confinement must be for it to be considered an adequate fault.