oc debug node uses registry.redhat.io/rhel7/support-tools, but this container image is only available on AMD64. It should be updated to use registry.redhat.io/rhel8/support-tools, which is a multi-arch container image.
I don't want to move this bug into verified without understanding the reason it has been marked as "Modified"; however, I was able to verify this by building a local oc client off the master branch and using $ oc debug node/*** to connect to a remote node.
Worked for me!
Apparently we can't support RHEL8 container images on RHEL7 nodes, so the current solution isn't going to work on RHEL7 workers. We are going to try to get the RHEL7 support tools built for s390x instead.
*** This bug has been marked as a duplicate of bug 1795277 ***