Yes, the effects stack.
To add insult to injury, they stack in the most beneficial order, so you halve any damage and then reduce the result by 10 (unless the attack was something that bypasses the DR).
One question, though... what kind of incorporeal monster has a DR 10 / good and cold iron?
Not only do they stack, but you apply the half damage first, then the DR.
Edit: Ninja'd by MA.
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The half damage is because some of the time, even magical weapons just swoosh right though the incorporeal critter without making any contact - in the old days, it was a 50% miss chance, but in Pathfinder we just cut the damage of every attack in half to simulate this.
The DR is because the critter you have in mind is especially evil and fiendish, hence only certain types of weapons (good aligned weapons made of cold iron) can hit it for full effect.
Two different things.
They stack.
The only question is, which goes first, the half damage or the DR?
Let's say a PC hits this monster for 18 damage. If you apply the -10 and then half damage, he at least does 4 damage. If you do it in the other order, half damage and then subtract 10, his damage will be 0.
It seems that the first way is the only fair way to do it. In the old days, half of our attacks missed for 0 damage, the other half hit for full damage and we applied the DR to that, so half of our attacks still did a fair amount of damage after DR. I think it should still work that way, so DR first, then cut the damage in half. But I don't know of any RAW that supports that assumption.
Edit: It seems James Jacobs disagrees with my assumption, and he's far more worthy than I am. Still, it seems to me that his interpretation gives a huge jump in power to incorporeal creatures with DR (compared to the old days). I would expect that, using his interpretation, any incorporeal creature with DR may very well be overpowered for its assumed CR, so be careful using them this way, unless your group enjoys TPKs or long and frustrating 20-round encounters (followed by lots and lots of Restoration spells, no doubt, if they survive such a long fight filled with energy drains).
DM_Blake, I agree with you that incorporeal undead are probably slightly under CR'd. It's telling when my RotR players most tense moment in chapter 1 was not fighting Nualia, or even Malfeshnekor, but rather the 3 shadows.
I agree with DM_Blake - DR then halve for incorporeal (and this has been hashed out before btw, to no final resolution). It matters because of a change to the incorporeal quality made to streamline the system (halving damage instead of 50% chance to hit). It was not to make it more deadly in combination with damage reduction.