it is copyright infringement if a person uses assets they do not have permission to use, whether for commercial reasons or not. there are exceptions, depending how the assets are used (parody, etc). however, even that does not stop the copyright owner from filing an infringement claim or a cease and desist order should they choose to do so. the owner may also file a lawsuit for compensation from perceived damages.There's been a bunch of games like Corrupted kingdom that are using the character creator of koikatsu or other illusion games to make the models of their own characters.
Is it even legal to do so while profiting from it through sites like patreon and subscribestar?
They cant even prove the games were made with their software. Maybe all the renders are from blender and they just happen to look like honey select. They got nothing thats why they dont do anything.It is completely illegal.
Under both Fakku and Illusion's terms it is banned to use their assets, including screenshots, character models, basically everything to "generate money".
Are you likely to be caught or have action taken against you, not really, but in terms of legality there's no grey area, it is a completely black and white issue and it is banned.