Right, After some extensive testing this is what I've found:
Getting snapdrive over NFS working is not too difficult but the following must be observed:
1. The server must be able to connect to the VSC tool
2. The NFS areas must be held on the phyiscal filer and not a vfiler
3. VSC must be able to see the volumes that SQL uses - best way to test? Take a VSC backup of the volume. If it works, its good to go.
4. on the SQL server run the command sdcli smvi_config set -host [IP Address of host VSC sits on]
5. Net stop snapdrive, net start snapdrive
6. Launch snapdrive and marvel at the VMDK(S)'s sitting in there.
If it doesn't work then something on the list above is missing/unconfigured/wrong version. For refernence I used Snapdrive 6.4, SQL SnapManager 5.2 and VSC 4.0