The tool your describing sounds like the extrude tool. which will extrude a profile along a path. Loft in maya will bridge 2+ profiles in order of selection.

I presume you are outputting polygons since you are using the fill hole command, this will just make a single polygon at each hole.

No new meshes are added to do this, it is not the same as using the planar opperation in NURBS (surfaces) which would create a new surface. All the planar tool does is create a polygon using existing verticies so no fusing is required.

You would only get 'visible seams' if your output was NURBS since commands that fill the hole such as planar do create new geometry (thats just how NURBS work) however as long as your tesselation settings are correct the seam will not be visible at render time.
The out put however will often be an n-gon so you will need to use split polygon to go in and make a tidy result.