Your question seems a little unclear to me. It is possible to sort images that have been imported into the Lightroom catalog regardless of whether they have been processed by Lightroom or not. But they do need to be imported into the catalog so that you can see them.
I'm assuming you mean "isolate those that have not been processed", as opposed to actually sorting them.
If so, then yes:
* but you have to use a smart collection (not a sort, and not a lib filter), which has a rule: Develop -> Has Adjustments.
Worth noting: if you apply a develop preset upon import, then photos "have adjustments" upon import.
Another option if you shoot raw is a script (not a plugin) called:
* Select Raws Without XMP.
If you have XMP saved automatically, then "raws without xmp" is equivalent to "not adjusted since import".
If you save XMP manually, then "raws without xmp" also includes those you neglected to save after editing (worth knowing about..).
Of course if you don't save xmp, then it's useless .
If interested: Misc Scripts (it's free, and I wrote it).
If not interested: Please don't think ill of me - I'm not pushing this script, but informing of it's existence, in case you'd find it useful, or it inspires other ideas..