Considering the components are CC0, and they are derived from CC0 components, In my honest opinion, stuff generated by that tool would be CC0. Good job connecting the dots. I couldn't find the relationship between macouno's parts and greyoxide's parts until you provided that link.

As for "concluding for sure that it can be used in a commercial game without legal risk"... well, my honest opinion doesn't cover that, I'm afraid. You'd want to talk to a lawyer for that kind of surety... or the author, macouno. But I know you already tried to contact him and have gotten no response. :(

Hmm... I was assuming that since the tool's author was using CC0 assets and did not specify any (other) license, he would give it the default license of CC0. That isn't an assumption I should make, though.

On the other hand, software tools do not typically change the license of the asset being derived. Using Photoshop on a CC0 picture doesn't make the picture subject to the Adobe EULA. Using a macintosh laptop to produce synth music doesn't force the resultant song to be under Apple's OS software license. Usually, the output's license is determined by the input's license plus any additional restrictions you, the user of the tool, are permitted to add (if you so choose). Is there reason to suspect this tool is any different?

I would think that if you took a CC0 public domain work and then created a derivative work based on it that you would then be able to apply whatever terms you wanted to said derivative work becase it would be yours.

Normally derivative works are still basically owned by the author of the origional work unless you can convince a judge otherwise. How easy that is varies quite a bit. Great leeyway is usually given for satire and social/political commentary but just adding an extra note to a Metallica song does not give you your own Metallica song. But in the case of CC0/public domain works there is no origional author from a legal/copyright perspective.

So I would think that any derivative work derived from a public domain work would by default fall under normal copyright unless the author of the derivative work stated otherwise. For example the story of Goldilocks and the Three Bears is clearly in the public domain yet the TV series Goldie and Bear, although derived from the origional public domain story, is clearly owned by and copyrighted by Disney.

The real questions would be what constitutes a derivative work and at what point does the author of the origional work loose control over the derivative work. This is really something that should be discussed with a lawer.