By definiion iLO is not a STONITH device, it is a management engine. It can be used to remotely power off a server, so it can be used for this function.
I'm not familiar with pacemaker or its utilities. One thing I would suggest is to use external/ipmi instead of external/riloe. The underlying bits in iLO have changed over the years, and this python script may not work properly.
To understand what some of the values are that you're trying to figure out, you might look at the python scripts in /usr/lib64/stonith/plugins/external/riloe and /usr/lib64/stonith/plugins/external/ipmi (locations may differ a bit depending on what distribution your using)
if you decide to try ipmi, iLO3 and iLO4 require the "interface" to be lanplus, and the user priviledge level needs to be set to operator at a minimum.
Using this syntax I was able to shutdown a Gen8 server over iLO4
stonith -t external/ipmi hostname=labunit1 ipaddr=xx.xx.xx.xx userid=admin passwd=pword interface=lanplus -c 4 -T off labunit1
labunit1 doesn't really mean anything, but it wouldn't work without something in those 2 fields.
You need the -c option set to at least 4 or the command will fail
Hope this helps