hi,
it is standalone, local account. You will not be able to use AD password for it. This is what is written about Client Administrator in the guide (https://support.symantec.com/en_US/article.DOC9133.html) on page 41:
Provides the local support to Symantec Endpoint Encryption registered users. You create client administrators for Drive Encryption. Client administrators cannot change their own passwords or use any password-recovery methods.
However, what you can do is to use the same Client Administrator credentials for other packages you create (you can export clients administrators to csv, import from csv or load client administrators from installation - msi file). This is described on page 76 of the same guide.