If I understand your question, you have seen the enhancements to Camera Raw, and realise you can do a lot of things in ACR that you used to do only in Photoshop. But when you talk about Smart Objects, I'm not sure how that fits in, as they aren't really anything to do with ACR, and I don't see any benefit to using them in an Action. So based on what I think you're saying, I'll try to explain myself.
First, Smart Objects. These only exist within Photoshop - you can think of them as a special type of layer. They cannot be saved separately from the PSD file. While you are in Adobe Camera Raw (ACR) there are no smart objects. You are just doing non-destructive changes to your raw file, exactly the same technology as Lightroom uses to edit raw (as @cadmium pointed out). Once you enter Photoshop, smart objects are an option that can make certain types of adjustments easier to tweak later - mainly useful if you're doing lots of certain types of work inside Photoshop.
Here is a quick outline of how the workflow might be in two scenarios.
Scenario 1 - all adjustments done in ACR
If you do all your adjustments in ACR, and simply want to resize/convert to JPG, you can do that via the batch processing in Photoshop. You don't need a Smart Object to do that. The easiest way would be to do all the raw editing, and click Done in ACR when you've finished each file, possibly sync some files (see below) then from Adobe Bridge, select all the files you want to resize/convert, and use Photoshop batch processing to do that for you. No need for PSD files at all, no need for smart objects.
Scenario 2 - some adjustments done in Photoshop
If you are going to use Photoshop to do further edits, you can then use Smart Objects in two ways.
The first is to Ctrl/Cmd click on the Open button in ACR. This will open the image in Photoshop as a Smart Object. You could then add adjustment layers in Photoshop, but at any time, double click on the Background layer (which is the smart object) and it will re-open ACR and let you adjust your RAW settings. Note however that you cannot do certain edits to the background layer (say cloning or healing) without rasterising the layer, at which point it's no longer a Smart Object - so this ability to go back into ACR is limited to certain types of edits).
The second way you can use Smart Objects is on other work-in-progress layers in Photoshop. Convert a layer to a Smart Object, then you can do things like sharpening, or apply effects and filters, and go back at any time, double-click on the Smart Object and re-open the filter/effect and change the settings. So adjust the sharpening for example, if you think you overdid it. Again, you can't clone or heal on those layers, only apply global effects and filters, adjustment layers, sharpening and blurring and so on.
So in one case, the Smart Object can take you back to ACR and let you adjust raw settings, and in the other the Smart Object can take you back into a filter and let you adjust the filter settings.
If you have a Smart Object background layer (from ACR) and double-click to make updates to raw settings, those will be saved with the raw file. Any other changes you make in Photoshop will be saved in a PSD file.
What you can do is edit in Camera Raw, open into Photoshop using Smart Objects, apply sharpening to the Smart Object layer, then save the PSD. The next day, you can open up that PSD, double click on the sharpening filter and adjust the sharpening. Or double-click on your background layer and reopen Camera Raw and adjust the exposure for example.
Synching Raw Files
Just as Lightroom allows you to sync changes you've made from one file to another, Adobe Camera Raw has the same functionality. You can do this a few ways:
Open one file in ACR. Make your adjustments and click Done. In Adobe Bridge, right-click
on another image you want to have the same adjustments, right-click and select Develop Settings > Previous Conversion. That will copy the adjustments from the previous file onto the current one. This will quickly copy the adjustments without opening ACR.
An alternate way to do the same thing: In Adobe Bridge, right-click on any image's raw file that you had previously adjusted, select Develop Settings > Copy Settings. Then highlight one or more images you want to sync, right-click on those and select Develop Settings > Paste Settings.
Open multiple files in ACR. Thumbnails will be displayed at the left of the screen. Select one and edit it. Once you are done, Shift- or Ctrl- click the other image thumbnails, then click the Synchronise button.
When you sync, you can choose what adjustments you want to sync. That could be white balance and exposure only, or it could include things you've done with the adjustment brush (but obviously that only works if two images are composed exactly the same, as the adjustments will be applied to the same areas of the image)
This probably isn't quite as nicely integrated as in Lightroom, but all the functionality is there, and pretty easy to use, especially if you use Adobe Bridge to tie it all together.
Action to Resize/Convert to JPG
You might want to explain further, but if you want to do most/all of your editing in Adobe Camera Raw, then want a Photoshop action to resize and convert to JPG, then you don't need to use Smart Objects at all. They are only useful if you are going to be manually editing within Photoshop and want a safety net to be able to re-adjust a few things at a later point. If an action is going to open up a bunch of files, resize, and save as JPG, then Smart Objects not needed, just going to slow things down.
