I assume most of the demos and packs posted on geeks3d are creative commons (NON commercial use). Are there any demos that are MIT licensed?
If the shader posted on geeks3d (shaderlib or in the posts) is a simple copy with minor modifications of another shader, you have to check the license of the original shader (there is always a link to the original shader). If the shader author is Geeks3D (there is no link to a source, except if I forgot it...), yes you can use it as you want, I don't care. If you have a doubt, do not hesitate to use the forum.