fixed in spacewalk.github:
This bug only addresses not prompting for, or attempting, monitoring install when satellite version is 5.8. A subsequent fix will also prevent monitoring install when satellite proxy version is 5.8.
I thought that the issue is about situation when satellite has disable monitoring and prompt is not shown during installation.
1) disable monitoring on Satellite 5.6 or 5.7
2) run configure-proxy.sh
You do not have monitoring installed.
Do you want to install monitoring scout?
Will run 'yum install spacewalk-proxy-monitoring'. [Y/n]:
I suppose that correct behavior is that installation skip question about installation monitoring when the monitoring is not enabled on satellite.
I created new bug for previous issue - bug 1459121.
Verified with spacewalk-proxy-installer-2.5.0-10.el6sat.noarch