First, concerning multi-piece necks...
If you get a piece of suitable wood for the neck that is truly straight grained and well-seasoned, it will be stable. If the grain is uneven, or of the wood is not well-seasoned, you will get better stability by slicing the wood and reversing every other piece and regluing the whole.
Some manufacturers attempt to achieve the same effect by laminating woods of different species together. I, for one, don't think that this is a good solution. I understand the reasoning, but I feel that marrying woods of different species can introduce other problems. The foremost problem is that different species will react to RH changes differently. If you put them together you are asking for conflicts in dimension change when cycling through the seasons. In my book t is better to stay within the same species - in fact I would stay within the same lumber cut.
All of the best basses I own have once piece necks made of well cured, straight grained, and well cut wood of the same species - likely the same board. All are stable.
On to dual trussrods...
I am not sold on the value of dual truss rods. To me they are more trouble than they are worth. Once gain, I understand the reasoning behind them. But I haven't found any that corrected a problem that wouldn't be handled by a single, well-designed rod in a well constructed neck.
Others may have had different experiences, but I've been at this for about 50 years now, and have tried it all.
Instrument Technician, Toronto