Question about Xbox Music cloud syncing

Hi internets, I just have a quick question about Xbox Music that I couldn't find elsewhere. If I add songs to Xbox Music that aren't available through Xbox Music, are they visible on other devices, or is it only media available through the service. I listen to a fair amount of local artists that will likely not be listed, so the ability to upload music to the cloud (like Google and Apple) is a must have feature for me.

Thanks for any input :-)