Is there a way to use a grey scale image to mix 2 different noise textures into the displacement of a material?
For example black is one noise texture node and white is another noise texture node.
Like connecting a greyscale image to the factor input on a mix shader node will blend 2 different material nodes.
For mixing value/color information, you should use the RGBMix, not the mix shaders. You can use the image color as the factor for mixing both noises, and connect the mixed output to the displacement socket of the output node.
Can you clarify why do you mention UVmaps in the title? It’s misleading, when your question is just about mixing two values.