Adding libraries to Emby server is a little different under DSM 7 in that setting permissions for the shared folders has changed some.
If you've ever tried to add a library to Emby and it wouldn't accept, then the permissions might be wrong
1. Give emby read/write permissions to the shared folder
Open Control Panel...Shared Folder in DSM on your NAS
Select your shared folder...Edit... and then under the Permissions tab select the dropdown box and change it to "System in