I think there is no limit in VMware vSphere for NFS datastores.
You only have the volume and file limit of your storage provider.
For example, with an NetApp FAS8200, you have the following limits:
* 100 TB NFS volume (means VMware Datastore)
* 16 TB maximum File-Size
This means you cannot provision a single VMware disk with more than 16 TB (for real, it must be a bit smaller).
Hope that helps 🙂