You can run one DC engine in a consist with DCC engines but there is no way to speed match the whole consist like you can with all DCC equipped engines. If you're lucky, the gearing will be close enough so it will work but, most of the time, it doesn't.
All the engines do not have to be facing the same way. You just change a CV in one you want to run long hood first so the decoder recognizes that is forward for that consist. When you deconsist the engines, you change the CV back to short hood forward. If you set up your consist with software like Decoder Pro, you just tell it which engines you want to run in what directiona and the computer sets everything up for you. The combination of JMRI, Decoder Pro (both free software) and the Digitrax PR3 interface are a great investment if you're going to really get into DCC.