I have to agree with those who discourage doing it. You certainly could build a game with stock assets and release it commercially. Likelihood of being successful doing that? I have to imagine it's pretty close to zero. It has nothing to do with the stock assets not being good. They actually do look pretty good. But your work would not be original. As far as the process of building a game or application goes, yes, coding is the most important part. But when releasing something commercially, what's most important behind the scenes isn't necessarily what's most important for the user. When I play a game I want to play an original game with an original art style and original music. Nearly everyone does. All it would take is one game to get recognition using stock graphics, and then all other developers who tried to do it would be called out for using the same sprites and textures of that other game.
You could, but I wouldn't encourage it if you actually want your game to be played.
