is this a theoretical question, or do you have experienced any issues?
The DCOM hardening patch will NOT EFFECT the UaGateway because UaGateway is configured to run LOCAL ONLY connections without using DCOM.
UaGateway was designed to migrate classic OPC installations, but (of course) is intended to use secured OPC UA remotely (over the wire). The (potentially insecure) classic connections will be configured locally on the same PC only, where the hardening patch has no effect.
Therefore, if you have used UaGateway as intended, there will be no issues with the DCOM hardening patch from Microsoft.
See here how to configure UaGateway: