Apparently ADMT doesn't migrate passwords for service accounts even if you installed and configured password export service on DC.
So, what would be the best solution for passwords? Resetting them after migration?
Below is from MS article:
The password is never migrated when a service account is migrated. Instead, ADMT uses a clear-text representation of the password to configure the services after the service account migration. An encrypted version of the password is then stored in the password.txt file in the ADMT installation folder.
After the service account is migrated, ADMT configures the service on the workstation or the server to use the new password, and the service will now start using the user account in the target domain.
If you miss a service account that shares an account with a service that has already been migrated, ADMT cannot synchronize the service accounts. You must manually change the password for the service account and then reset the service account password on each server that is running that service.