Honestly, I'm new to this whole transferring thing. My first hand held Pokemon game was FR, then Pearl, and now SS. So I'm still a little fuzzy with the details on transferring.
Yes, you can trade back and forth between DPPt and HG/SS with no problem at all.
You can do it quite early in the game too - after obtaining the regular PokéDex.
Please, use the HG/SS Help Thread next time for any more questions, thank you.