If a smelter is placed on a tile and I attempt to use the "Place" command to move it somewhere else on the same tile, I get the following message, as if trying to move it to a tile with another smelter:
[22:26:57] You cannot place that item here, since there is not enough space on that tile.
Presumably this happens with all one-per-tile limit items, but a smelter is what I can verify right now.