I don't know of a way to provide SMTP authentication for Dell OpenManage. I can give you a couple of work arounds though.
The first one, is allow unauthenticated relaying only from your OM server's IP address. This should be done carefully so as not to create an open relay for the world. The process to do this will be different depending on what mail server you're using.
The other option only works if you're sending email to users on a single server. If that's the case, just use that server's name or IP address in the SMTP configuration as the SMTP server name. Mail servers always accept anonymous connections for email directed to a mailbox they hold.