You actually dont need to mirror the accounts in OD. If you bind the server to AD (basically the same way you do via Mac OS X client) you can place the AD users that need access in groups on the OD server and give them access. I’ve been doing this with a podcast server in our implementation. If I remember correctly it can even take advantage of SSO so they wont even need to type in their credentials, it will just use their kerberos ticket for authentication.
Then if you have additional non-AD people that need access you can create those accounts in OD and mix them together in groups to give them access.