The default Rec.709 VLUT in Nuke is just a 1D LUT, which clips any values above 1. It is the Rec.709 camera encoding curve, so if your linear working space in Nuke uses Rec.709/sRGB primaries you are creating the equivalent of pointing a simple Rec.709 video camera, with no highlight roll off, at a scene containing the (relative) scene-referred linear values at the end of your comp. This is not an approach I would recommend, and I would even go so far as to say that in my opinion the inclusion of that curve in Nuke was a mistake which they now only keep for historical compatibility reasons.
The ACES Rec.709 Output Transform is a a much more sophisticated display transform, which includes a colour space mapping from the ACEScg working space to Rec.709, and tone mapping to expand mid-tone contrast and compress the shadows and highlights. The aim of this is to produce an image on a Rec.709/BT.1886 display which is a good perceptual match to the original scene.
The Rec.709 Output Transform is designed for a screen which conforms to BT.1886, so you should calibrate your screen to that (or to a pure gamma curve if you are of that school of thought.) You calibrate to the display standard, and the Output Transform targets that. You do not calibrate to the Output Transform.