Licensing is not an issue. It is simply just a plugin similar to the plugins made for RPG Maker MV/MZ etc, and there are many on here which are not officially made by RPG Maker such as the Visustella plugins (essential plugins). The issue is RPG Maker Unite. It's just not up to quality standards in its current state. The developer of this plugin should have made the plugin/addon for RPG Maker MZ which is a solid engine, has a better UI, has better workflow, has a much larger amount of users using it, it has a lot of plugins and plugin support, and it works properly! I don't see RPG Maker Unite getting the same amount of plugin support (actually much much lower), especially since the Visustella team has said that they will not be creating plugins/addons for it. The dev of this plugin should seriously consider just switching this plugin over to MZ. It would be more profitable.
Viewing post in Unite Add-on - 3D Dungeon comments
Except there's already 2 well known plugins for MZ for 3d environments.
Rose Engine
and
MZ3D.
It'd be kind of redundant to make a third 3d environment plugin for MZ.