The only effective defense against a rabid bear is to put it down, and for that, a significant firearm is needed. Thankfully, rabid bears are very very uncommon.
I would say that this is plausible, but do we know this? Are there instances where rabid bears were undeterred by bear spray?
As for other rabid critters, it is only prudent to avoid contact with any that show any abnormal behavior - simple, easy,and effective.