Ipmitool is a robust and generic tool for finding specific system information. It is generally possible to get the serial number of a host using the ipmitool command. Ipmitool has several options available that can give you very specific information about your host. In particular the fru command. An example of using ipmitool fru is
ipmitool -H <host_ip_address> -U <username> -P <password> fru
This will provide a very detailed listing of system parameters. The relevant one for getting the serial number is the “System Serial” parameter. You may be able to grep this out from the output, or do a manual viewing. Each ipmitool fru command will likely produce different results, so sometimes a manual lookup can help.