In UE4 you can do snapping to vertex.
Press “V” to activate temporary vertex snapping. Or Setting->Enable Vertex Snapping for permanent.
But 4.7 and 4.8 have little differences for translating pivot.
Move pivot - position mouse cursor over white ball in widget of transform and with middle mouse button move the pivot.
For snap first object to second - with MMB and “V” key, snap pivot to needed vertex. Do not unselect, because pivot transform will be reset. With LMB+V, snap first object to second.
Work only inPerspective view.
The pivot can now be positioned in both perspective and orthographic viewports
Dragging the translation widget with Alt+MMB will move the pivot location in any viewport mode.
But, i think it is a bug, temporary snapping for pivot not work. And you need activate Enable Vertex Snapping in Setting.
For object snapping temporary mode works normally.