If you are asking about this as a backup target device accessed over CIFS then whilst it can be done it is often difficult to sort out the security so that access is allowed. If you can present some storage over iSCSI form teh NAS device it is usually more reliable and easier to configure.
If you have to use CIFS then the service accounts used by Backup Exec have to be able to acces the UNC path to the CIFS share which kind of means the Data Domain device will need to use domain authentication so that domain accounts against the services can be given full access. There also can be difficulties caused by differnces in SMB levels between OS of Backup Exec Server and that offered by the DD device and this may mean you have to adjust the NTLM security to allow mixed authentication levels.
