Sammy,
As Trainerjet pointed out, it seems you have your alternate requirements a little mixed up. If *B* is doesn't meet the 1-1-2-3 requirement you must list an alternate. The alternate, *C*, must be forcast to be better than 600' and 2 miles if it has an ILS, or 800 and 2 miles if it has a non- precision approach.
Is this legal? Absolutely, you have filed a legal alternate, C, and presumably have sufficient fuel. All the legal requirements are met. Nothing says you MUST go to C if you go missed at B. In the air, you do what makes the most sense based on the current situation and the current observed Wx.
Is this safe? Probably. D may not meet the requrements for an alternate, but it may be plenty safe to shoot an approach. Remember, D wasn't used as an alternate because it was *forcast* to be below 600/2 or 800/2 as required. An ILS with a 600 foot ceiling is a pretty safe bet, and besides, that was the forecast Wx, the actual Wx at D may be better after you go missed at B. The only time I would question the saftey of this, would be if D was really on it's butt, and you had little chance of getting in there legally, or if you were close on fuel and shooting an approach at D was compromising your ability to continue safely to C.
regards