Hi,
You can connect multiple compute clusters (HA&DRS) to a single datastore cluster.
Please try to connect all the datastores to all the host in a single cluster, otherwise the cluster will be considered partially connected:
But I think this article will help you the most: http://frankdenneman.nl/2012/04/19/connecting-multiple-drs-clusters-to-a-single-storage-drs-datastore-cluster/
The limit is not the datastore cluster itself but the connection limit of the datastores.
For VMFS 64 hosts could be connected to a single VMFS Datastore, I'm not aware of any host limitations on a NFS datastore, I think thats provided by the NFS array manufacturer Please check the configuration guide for the maximums for NFS and VMFS just to be sure.
I created a series of articles on the design of a datastore cluster, you might want to check this series out:
http://frankdenneman.nl/2011/09/16/architecture-and-design-of-datastore-clusters/
http://frankdenneman.nl/2011/10/07/partially-connected-datastore-clusters/
http://frankdenneman.nl/2012/01/impact-of-load-balancing-on-datastore-cluster-configuration/