There are 3 levels of DRS:
1. Manual
2. Partially automated
3. Fully automated
When you first configure the cluster you set the default for all the VMs in the cluster. You can also change this Cluster level default at any time.
Once you have VMs in the DRS Cluster you can view the cluster properties and see an option under 'VMware DRS' - ' Virutal Machine Options'. This allows you to set the per VM DRS automation level. So you can set you VC VM to Partially automated or Manual and it will be excluded from being moved to other hosts automatically for load balancing. It's not completely pinned to a host since you can still move it using manual VMotion.