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.
