In theory, synchronizing password as opaque string would work as soon as long as the password hashing scheme are supported on both sides.
However, I think AD wont let you retrieve the password even when it is hashed...
My 2 cents
Thanks for the update. What will be th ebest option will you recomend?
How do you plan to use the passwords on the OUD side ? IS it for EUS ?
Do you really needs passwords stored locally on OUD or would path through authentication provided by OUD work for you ?