Thanks for all the tips. I think I must not have explained my problem well enough. I do use a Bahtinov mask and I do not move from focusing on the moon to the assumption that a DSO would also be in focus. I can clearly see the DSO in the eyepiece. When I swap out the eyepiece for the DSLR, the DSO, after adjusting time and ISO, cannot be seen for focusing. I've been able to get images of the DSO via trial and error--thank goodness for digital photography. So, I guess my question is: Why can't I see the DSO through the camera viewfinder or the live-view? Again, thanks for the help.
The eyepiece and DSLR will focus at different points, often very different points. So simply swapping out the eyepiece for the camera will likely be so out of focus that nothing will show.
Most DSO objects are really really really really dim. You will never see most of them in Live View, as the camera (mine, at least) will drop the exposure to something like 1/30 sec, which is far far too short. If you max out the camera's ISO (12,800 on my Nikon), you should be able to see the brighter stars in Live View, enough at least to focus. Note that the Bahtinov mask is intended for use with the camera, not the eyepiece.
With the Moon out right now, I'd use that as the initial object to focus on. Do it in the terrestrial manner, getting it as sharp as possible in the viewfinder or with live view. You'll need to shorten the exposure a lot, of course, and probably reduce the ISO. Then move the scope over to a bright star and with both the camera ISO and the live view exposure at maximum), see if you can see a star in live view. If so, use the zoom function on live view on maximum, and focus it a bit more (going for the smallest star you can get). Then try the Bahtinov mask to see if you can make out the spikes. If the star is bright enough, they should be there, otherwise you'll just have to use the minimum star size method.
At that point you can start imaging. Do it at first with the camera still at max ISO, putting the camera exposure back up to, say, 30 seconds (it's the most mine will do on its own). It will be grainy; that's ok. You're trying to get some sort of an image of a DSO object. That will prove that you can aim and track the object, and give you an idea of what sort of exposure (combination of ISO and shutter time) you need. Aim for one of the brighter objects; M13 would be good, though it's kind of close to the Moon right now. Maybe in a week it will be out of the way enough for imaging. Whatever you do, don't try to go after a nebula right now. Too much Moon, too dim an object, and unless your DSLR is modified, it's likely that the built-in filters will remove all the nebula's light anyway.
Pre-posting EDIT: Kathy types faster than I do... But I think we're both suggesting about the same thing. Bottom line, you should not expect to see a dim object in Live View.