It is never OK to disable or not use DRS in a vCloud Director environment. Its only OK if your in a small environment of several vApps. Trust me, don't disable it, use it. I have seen clients not use it and the cluster was so imbalanced it caused severe resource contention and the clients couldn't work.
If you want to balance the cluster its best to calculate and use the percentage as a cluster setting in DRS and not the host tolerates setting. Read the VMware vSphere 5 Clustering Technical Deepdive by Duncan Epping and Frank Denneman. Its a great reference.