X-ray changes the way chuncks and ore are send in packages to client.
When an ore is encased in stone without an air pocket on each side the ore will show us as cobble.
And the x-ray texturepack/x-ray mod will not show it as ore.
But, when it is in a cave or something alike. the x-ray mod will still show it up.
So because of that it is still possible to use x-ray to find gold pockets.
not going to elaborate how