The skin tone line on the new vectorscope is not changing to accomodate the variations in numerical value of skin hue depending on the working color space.

If the working profile in both Photoshop and ACR are the same, the skin tones match the proper hue when a photoshop image is brought into ACR.  However, the skin tone line on the new vector scope is not moving to adjust for the fact that the Hue value associated with skin tone varies between color spaces.  The skin tone line seems to be set at a hue of about 18 regardless of what the working export color space is, so it gives incorrect skin tones unless you are exporting to Rec709. space.

Open an image in photoshop with skin and convert it to Rec709 color space.

In the settings panel ensure that ACR working space is also Rec 709. 

Open the base layer in ACR and select the skin of the subject.  The skin tones will properly align with the skin tone line on the new vector scope, at a hue of about 18-19 degrees. 

Now, cancel in ACR and use the Edit menu to convert the image to ProPhoto color space.  In the settings panel, change the settings to ensure that ACR is also exporting to the ProPhoto color space. 

Open the converted image in ACR.  The skintone will show up properly on the vectorscope, at a hue of around 31 degrees, consistent with ProPhoto, but the skintone line has not moved to reflect the current working color space.   

I tested also with Adobe RGB 1998, for which the skin tone should be at about 22 degrees, and saw the same problem.  

I am attaching two screenshots and an ai generated photo of a fake person that i used to test.  

As an aside, the appropriate hue values can be obtained by beginning with a skin tone chart such as the one attached that I have created for ProPhoto, then converting it to the different color spaces using the edit->convert command in Photoshop, and reading the appropriate numerical value for the hue from the color picker.  So, it should be a simple matter to have a reference skin tone and then change the hue for the skin tone line in ACR to match the working color space.

I created the skin tone chart some time ago, using trial and error to match the Rec709 skin tone line in Final Cut Pro when the color space profile is embedded in the image and it is read into Final Cut Pro. The numerical values in the comments on it were those I derived by trial and error to match in Final Cut pro, but they are within a degree or so of what I get when converting within Photoshop, and thus within the actual variability of real skin tones.