Ultimately, anything produced by a creator cannot be distributed in a work other than the original context it was intended for until that creator gives permission otherwise.
This applies to all creative/intellectual property be it code, textures, models, or even text and dialog.
While we are an international community so it is difficult to say any specific nation's law applies broadly here, the community respects and applies these rules itself.
If the creator has not released their work for general use, typically via the LSP/OSP "license" our community uses, you will have to ask them for their permission to pack it into a new work and distribute it.
If your mod is dependent on a specific creation, you may want to release your mod as a sub-mod. That is, distribute your work (without the infringing content included) and install it over the mod you are dependent upon.