In activiti explorer you can see your "own" instances, i.e. the instances you initiated.
The activiti explorer is meant to be a kind of prototype showcasing the *potential*of the activiti engine. But it is not meant to be a full blown monitoring and administration solution. (One sometimes forgets this, since Joram and Frederik really did an impressive job with this webapp )
So I guess you could try to add the functionality you need to the explorer on your own.