Be careful when using the results of RV-tools.
I found that the number of false positive Zombies detected by RV-tools is so high that I read the results as "the VMs listed in the Zombie column may eventually be Zombies"
I dont think that there is any tool out there that can detect Zombies with the probabilty you would want - to be able to use the results for an automatic action - like delete the directory where the eventual Zombie lives in