After importing your height map you could use Unreal’s grid coordinate system as long as you lock the landscape to the grid. For example make the center be 0,0,0 or a corner. After that you can setup an array of transforms to hold all your location data. Only downside is you will probably have to manually setup exactly where each object will be, but once setup it would be specific.
Do you have all the object locations already defined? Also how large of number of objects do you have roughly?
If you need something incredibly detailed, here is a guide on how to get accurate terrain using a geographical information system, and the logic behind it: Real-world Terrain Visualization with Unreal Engine
Free GIS Plugin: https://forums.unrealengine.com/community/community-content-tools-and-tutorials/1438893-plugin-import-gis-data-into-ue4
Guide on how to use said plugin to import heightmaps from real geographic information: Creating Real World Landscapes in UE4 from Maps (GIS Data) - YouTube