Why would you use displacement on that?
Seems to me to be a waste of CPUprocessing/rendering time.
vray has very good bump mapping if you clean up your bump maps and increase the contrast in Photoshop.
Vertex welding is a good solution in this particular situation but it wouldn't solve your problem when you use displacement on a flat plane (like on a furry carpet or grass mesh)
I once read somewhere that a more effective solution would be to have a black edge border (a few pixels width) around your displacement map which will tie the displacement down in that region (you can easily and quickly do this in photoshop.
And in the case of a tileable map, then you would create a geometry border around the actual plane, face or geometry that has to be displaced and then using the multi-subobject material, create a displacement map from your displament shader that has a nondisplaced material to go on that edge.
But like I said before, dispalcement is a very processor heavy procedure and you should only use it sparingly where you can't fake bumping with the bump map, otherwise you're just killing your rendertimes with that.