OK let me try and see if im understanding correct.
You have two layers.
an object on layer 1.
And an object on layer 2.
you want only layer 1 to be drag and drop when on layer 1, and NOT the layer two object?
if that is what you are asking.
My advice:
create a global variable "activeLayer"
if object is on active layer
Enable drag and drop.
Else
Disable drag and drop.