here is a new topic I can not solve. I am using Blender 2.80.
At UV Editor I would like to align vertex from one Object to Edge of an other Object.
I tried snap incremental. But each vertex will always snap to t's own incremental mesh?
If you want to do it manually just enable edge snapping, then grab the one you want and while moving it tap X to restrict the movement to that axis alone. That way, you can move horizontally and snap it to the same place the vertex on the bottom is, while maintaining it's vertical position unchanged.
All that said, I would simply add a few UV seams along those horizontal loops.
As I could not find snapping to edge in UV-Editor (see comments below), I made a "work around". Select all Vertex of one line, then "align to X" to all bring them in one line. After they are all in one line you have to pin the line. Then use "snap to Vertex" grab botten vertex of "high poly mesh" and snap to vertex of "low poly mesh".