I solved this same problem, but Blender-specific way, for a game a while back by having adding special handling for splines to the Blender export script Unity ships with + a custom import script.
The Blender export would export the spline with multiple Transforms that were a fixed distance apart and numbered, then the import script would find splines and spit out a ScriptableObject listing each point, so the camera's position and rotation were a lerp between 2 of the transforms (since the exporter took rotation along the spline in Blender into account). It was somewhat quick and dirty, but it worked well enough with letting artists change areas of the camera track that didn't match the levels' tracks
The Blender export would export the spline with multiple Transforms that were a fixed distance apart and numbered, then the import script would find splines and spit out a ScriptableObject listing each point, so the camera's position and rotation were a lerp between 2 of the transforms (since the exporter took rotation along the spline in Blender into account). It was somewhat quick and dirty, but it worked well enough with letting artists change areas of the camera track that didn't match the levels' tracks