Hello,
My ancien team has made some configuration like these with 10.6 and Ontap 8.0.1. It was possible but as far as I now not supported by either NetApp or Apple. You have to use the LDAP integration of the CIFS setup and some additional steps. You'll find more information on this thread : https://communities.netapp.com/thread/1888
As the CIFS emulation in 10.7 has changed (now a proprietary implementation from Apple) I don't know if it works with 10.7
You could have used NFS (especially if they are no Windows PC at your customer)
As far as know Time machine only supports AFP for NAS targets from Lion (10.7), there are workaround though like this one :
http://basilsalad.com/how-to/create-time-machine-backup-network-drive-lion/
I guess you'll have to pass some times with the customer to test the various possibilities in his environment. I hope you have forecast some hours/days of service ...