I purchased a watch for myself from a company on DH, fully knowing it was fake and using it for my own personal use.
I can tell you that I had no problems with the transaction, in fact I have had the watch now for a year and it hasn't missed a beat, and people have no idea that it is not genuine, it's a very impressive product.
That's just one experience, it's always a risk when dealing with Chinese companies, if in doubt just start off small and judge for yourself.
I believe most of the scammers will only be dealing in fake brand names anyway, if you are looking at purchasing no name products then the chances are very good that the company is genuine. That's still no guarantee that you will recieve your products of course, even the most reliable companies in the world cock up every now and then, but at least you will have a chance at getting some satisfaction with open comunication.
I'm not sure if DH has a forum or not, but that would be an excellent place to learn more about the company. If not I would suggest taking a look at other sites like aliaba.com and tradekey.com. Very helpful forums there to weed out all of the suspect suppliers within the group.