I think so, yes.
Open-back dress is a very distinct dress, mostly evening_gowns should fall under this tag, though (post #2836229, post #2917150).
But also when the upper back is exposed, this tag still fits (post #2920490, imagine it wouldn't be see-through).
Backless outfit might apply to attires that are not dresses (post #2922520, post #2909919)
Back cutout however is for attire that do cover the back normally, but have a cutout. You might compare it to navel_cutout for the stomach area (post #2903986, post #2898353)
Those tags can be subsets of each other, but not necessarily.
Backless to me seems to be the same as backless_outfit, so I would alias that.