I don't expect them to be the same:
- When you open a DNG/RAW in ACR there are a few things that happen under the hood which are not necessarily linear, such as automatic invocation of highlight recovery, especially with process 2012. This difference is more evident if you have an image with overexposed or even clipped areas.
- When you use the PS Camera Raw filter, you just open in ACR the rendered Photoshop image (not the original RAW), which is bounded between 0-255. Another way to see it is that the RAW file might have highlights and shadows beyond the tentative rendering, which can be used for highlight/shadow recovery and the tiff/rendered image don't.
Try this: Save your image in Photoshop as a 16 bits Tiff, Prophoto RGB and repeat the experiment using this file
I mean: open the tiff in ACR with no adjustments to PS, then open again the tiff in ACR, adjust exposure and then Photoshop. Now back to the previous file and use the Camera Raw filter and adjust exposure: You will find that both files are identical, because the input to ACR was essentially the same, a rendered image not a RAW.
If you want the capability of doing adjustments after you have opened the image in PS use Smart objects (of course, ACR will not show any adjustment made in PS)