Hi,
Can you please confirm whether it is iDRAC6 or iDRAC7?
Also while creating the discovery and inventory task, please make sure that Secure mode, SkipCN check, Trusted site is selected.
Also can you try running this command on the target IP and verify if it return some values:
winrm e cimv2/root/dcim/DCIM_SoftwareIdentity -u:<username> -p:<password> -r:https://<IP Address>/wsman:443 -SkipCNCheck -SkipCACheck -auth:basic -encoding:utf-8
Please let us know.