Some royalty free and publicly available assets do not allow redistribution. Which means, these assets cannot be placed in a public repository. In such cases is it fine to just have some placeholder assets in the project repo (with links to original assets) and use the actual assets only in builds published on itch.io.

Hopefully we can get an answer on this.  Several game artists have offered up their artwork for free and they have it on their site as such, they just don't want their artwork forked into other repos where credit can be stripped.