When doing a completely hands off Solaris installation the System Configuration profile needs to contain the hash for the root password, and the optional inital non root user.
Unfortunately Solaris doesn't currently provide a simple to use command for generating these hashes, but with a very simple bit of Python you can easily create them:
import crypt, getpass, os, binascii
if __name__ == "__main__":
cleartext = getpass.getpass()
salt = '$5$' + binascii.b2a_base64(os.urandom(8)).rstrip() + '$'
print crypt.crypt(cleartext, salt)