Hi Robin!
I had the same Question and I can did use the Register-via_GRLoader Operator whit the next parameteres:
On GrLoader Connection Options tab, on my environment the tomcat por is by default 443, i think that you should use the port tomcat
and on properties I copied the env.nx archive and paste it on a new folder ("E:/Cargas_CMDB/SDM)
Input file is the archive .XML whit the CI to update
after that I can run the operator and update the CI on the cmdb. I hope it has been helpfull