In situations like this it's odd to me that the rightsholder wouldn't just sell an official build of the FOSS reimplementation with the assets (legally) included. If some of the proceeds end up going toward the FOSS reimplementation's donations then it seems like an easy win-win.
There are actually cases this has happened in (e.g. re-releases using ScummVM under the hood; id basing products on community source ports, etc.), but it's not always that simple. Chris Sawyer as creator for example is known to have particular opinions on this as I recall, and if you e.g. look over to film making there's also a hot debate over preserving original artistic intent and original creations over later rema…
When you get to the last, you can definitely see how the original creator/artists could disagree.