Humm this does not sound like re-targeting to me?
Re-targeting is used when the naming convention on one set of animations do not match the naming convention of another so the re-targeting of the animations would be “set1 > set2”
Targeting, as in the mesh shares the same rig and animation, then the first rigged character model would be the master and all other imported targeted to use it’s skeleton so would be “mesh1 < mesh2”
As I read it you want to target to an skeletal asset already in UE4 and the asset you wish to import shares the same rig then yes during FBX import you can tell UE4 to import using the rig already supplied.