In the ACM documentation, there is the following note for the cluster-proxy-addon:

Important: To use cluster proxy add-ons, you cannot have a cluster-wide proxy configuration on your hub cluster. 

In older versions of RHACM, there were specific limitations where Hosted Control Planes did not support being deployed if a cluster-wide proxy was active on the Hub because of how the API server traffic was routed.

This note needs to be removed from the 2.15 and later versions' documentation.