I agree with Neil. I do 95% of my image processing in Lightroom; (that said, scanning with SilverFast, there are good reasons to use a number of SilverFast tools first before importing the photo to the LR catalog). Photoshop is reserved for things Lightroom simply doesn't have the tools to do, and that is becoming less and less. But reverting to John's original question, there is nothing special about using DNG format or ACR for processing a scan. Underneath the DNG shell the image files are ordinary, rendered, pixel-based 3 channel RGB files, which either LR or ACR can process equally well. As LR and ACR have the same "Develop engine", there is no reason to use ACR if happy with the LR workflow from those drum scans.