You cannot use a single ETCNet2 node as a DMX merger. HTP arbitration works via node address not by port address. Port addresses on a node are arbitrated like version 3 where the lower the port # the higher the priority.
Imagine a scenario where you plug dmx jacks into ports 1 & 2 on a Net2 4 Port DMX Node and have configured them both as the same universe input:
This behaviour holds true for ETCNet2 DMX nodes and Net3 DMX gateways running in Net2 mode. A Net3 gateway running in Net3 (sACN) mode should be able to merge multiple input ports in an HTP fashion properly.