Technically you can. However the add-on was not designed with this purpose in mind so it can take some tweaking. The characters must be set up in the same way as the ones inside the add-on (have the same orientation and scale etc) to be instanced appropriately in a collection. To change the collection instanced go into the modifiers tab and switch the characters to your own collection.

We may work on some ways to make this easier in the future but right now it is not something easy to do within the add-on panel.

The Horde Add-on works with Blender 3.2 and their corresponding geometry node systems. We plan on keeping it updated with future versions of Blender as well.