But Creative Commons doesn't permit the use of the art past marketing. Not allowed to include it in the actual project for instance. Do I have that right?
None of the CC licenses that I know of distinguish between marketing and other forms of use. The CC licenses have a range of restrictions depending on the specific one used. Freesound has a faq at https://www.freesound.org/help/faq/#licenses-0 The actual name of the license pretty much tells you what the restriction is though.
CC can be great for a lot of things. The biggest issue is that many people require attribution which can be tricky depending on the project. But there are some good options for CC that work well.
Just curious, which kinds of projects make attribution difficult? The worst I can come up with is that you'd have to include it in the small print at the bottom of an ad. Most other things (software, videos, websites) will have a more discreet place to shove all your credits.
In general, I think CC-BY is fantastic. CC-BY-SA is typically useless for anything except open source projects.