Texture usage in other projects

So I've been working with SRB2 for over a decade now, but the more I think about it, the more I kinda wish I could work with some Doom textures in addition to what's supplied. Techbase in particular - I like how id designed the textures such that you could stretch or shrink them horizontally by splitting the linedef up, something a lot of our textures don't really work with.

That said, I wouldn't want to include textures direct from an official IWAD - copyright infringement isn't particularly cool (ignoring that we're basing a mod off of Sega's intellectual property, which is itself copyright infringement - I'm aware of the hypocrisy, yes). That's where FreeDoom comes in - it's basically Doom, redesigned from the ground up to be, well, free to distribute, and most of the textures are close enough to the originals to satisfy my needs.

So, just to confirm, if I wanted to use the FreeDoom texture pack in a non-Doom project (well, insofar as the Doom Legacy-based SRB2 is non-Doom), I'd be allowed to do so, correct? Obviously, proper credit would be due; would it be better to list out all the contributors to the texture side of things from CREDITS, or would just a special thanks to "The FreeDoom Project" suffice? I assume you'll want us to include COPYING in our distributable. And SRB2 is totally freeware, so I doubt we'll be attracting ire like some of the paid iOS or Android apps using FreeDoom content do (despite apparently being legitimate?).

Bear in mind, all of this is hypothetical; I haven't committed to including Doom textures yet. (Also, I'd probably have to cut some of the more gory textures, on the grounds that, while it's great for Doom - Episode 3 wouldn't be the same without that - it probably wouldn't fly in a Sonic game.) I'm just clearing up whether I can, instead of doing so, finding out I couldn't, and making damn fools of my teammates and I.

It's all good as far as using FREEDOOM assets are concerned.

Being a permissively licensed project you may use the art even in a closed product. You do need to include the license/copyright notice though