It should be possible for the user to navigate via the link to dynamic called process definitions if the call activity is currently running. (as indicated by the instance count marker). The greyed out link should not be shown in that case.
If the call activity calls multiple different processes, the called process definition tab should be opened.
This feature is not provided in the history view as that does not have a called process definition tab. (Such a tab might make sense in general, but would be outside of the scope of this ticket.)