netbackup isnt as intelligent as ntbackup when it comes to using exchange recovery storage groups :)
u need to redirect the restore
so, after selecting the mailbox store u want to restore
click action-->start restore
then on the 'restore marked files' tab, select �Restore everything to a different location (maintaining existing structure)�
In the destination field, modify the Storage group name, and enter the name of the Recovery storage group that was just created, if the default name was used, this should be �Recovery Storage Group�, meaning the whole field would be Microsoft Information Store\Recovery Storage Group', otherwise netbackup tries to restore to the original location (your live mailbox store), which would fail since the store is mounted and has '�This database can be overwritten by a restore� ticked on the Mailbox stores� properties
with regards to the other problem your having, with not being able to restore to the cluster name, we have an exchange cluster setup with each node installed as a SAN MEdia server, to make netbackup understand that the exchange virtual server name (cluster name) can point to either node, had to do some command line stuff using nbemmcmd, which is fully explained on page 114 of the netbackup high availability guide.... u might need to do something similar with the virtual server name when backing up exchange as a client
hope this helps