So you are asking if while you are in a Lucid State in a dream if it would be possible to find a DC, proceed to ask them to remind you when you are Dreaming, and then from that point on everytime you have a dream a DC will come up to you and tell you that you are dreaming?

Hmmm I don't think it would work, because that would somewhat require your DC's to be intelligent and carry a memory with them. More likely a DC would come up to you and say "Today Is Sausage, would like the ham?" , but that in itself could make you lucid.

But I don't think that your idea has a very high % rate of working, and if it did work I dont think it would work that frequently, but it is worth a shot I suppose.