Re: Integration of Alfresco Community 5.0.d and Activiti 6.0.
About the first point, I'm not expert enough on Zimbra LDAP and probably the final answer depends on the Zimbra LDAP implementation if it really standard or not. I hope someone in the forum can share his/her experience.
About the second question, Alfresco comes with an Activiti engine bundled into it. Considering this the answer to your question is probably positive.