You're not supposed to be able to free type the restore location - that's expected.
not sure what's up with it locking up - if it were a read only location or the like it would throw an error - all it's doing there is looking for files and directories to see if it's a valid backup location - not much else going on.
If you copy the files locally, does it work? If so there's something wrong with the share/UNC setup to your backup location I suspect...
Not sure what you mean by all user MBX's are failing - are AD accounts being created? Were they created already but didn't have mailboxes? If AD users are being created but mailboxes are not this is a RUS issue - DiRT does not have such great powers as to dictate that mailboxes are created or not - it asks the DirSyncSvr service to create AD users with mailboxes or bind to existing AD accounts and that's it - if the AD accounts are created without mailboxes then the Recipient Update Service (Exchange) is not flying and you need to investigate that seperately.
To be clear, DiRT is not creating the users or the mailboxes directly so the account you're running it under does not need such rights - as long as the directory services for Unity are flying right it should work since DiRt asks those services to do the heavy lifting here.
I'm assuming prior to doing a DiRt restore you created a test user via the SA and make sure they got a mailbox and were flying %100?
Aside from that, I can't speculate what's wrong with your system - sounds like something upstream from DiRT and it'd definitely be a good idea to open a TAC case.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.