In Darktable, in the Lighttable view, is it possible to select/view only images that have been edited?
Yes, using the collect images module on the left. Select 'history' from the left dropdown menu then double-click on 'altered' to show only those images which have been modified. Try Darktable's user manual page for a fuller explanation.
Additionally you can stack rules so you can narrow down searches, eg, by searching by a particular roll or folder and altered or unaltered.
I answered a closely related question here, too.
For a quick way to select the modified images in the current film roll, you can also open the [select] module on the right side. Click [select untouched] and [invert selection].
User manual reference: http://www.darktable.org/usermanual/ch02s03s05.html.php