Yes Free Transform has what was set during the place and you can see in the option bar if the layer has been scaled or is at 100 % width and height. You can also drag out guide line to the transforms bounding box. Then later measure the size or drop in a low opacity pixel in two diagonal corners to force the bounds to the png's canvas size. However if you don't add those pixels in a script the bounds you get is that of the bounds of the non transparent pixels and in an action Ctrl|CMD clicking the layers content in the layers palette selects the non transparent pixels.
My Photoshop Photo Collage populating scripts do not always fill an image area when they resizing odd shaped png images, However if the png is rectangular with transparent borders the script will fill the area with pixel for the scripts gets the bounds of the non transparent pixels, not the png canvas size. So resizing works well.
