I wouldn't put a leather conditioner on the dash. The leather is likely highly coated with UV protectants and my guess is any conditioner would not soak into the leather anyways. What it will do is soak into the stitching and degrade it over time, which obviously you don't want.
You can test to see if its coated by putting a drop of water on it, if it beads up and rolls off, its coated. If it soaks in, its not. I have never seen a car with a leather dash that wasn't coated, even if the seats were uncoated (Jaguars, etc).
What I would use is a solution of 6 parts water to 1 part woolite (many owners manuals refer to a "solution of natural detergent for wool" which is Woolite) in a spray bottle. Use that to gently clean the leather and then dry with a microfiber or terry towel.
If you absolutely must use something to protect it, I reccomend this:
Its expensive but the bottle will last you forever. This is a great "interior sealant" that leaves a very fine coating on all the interior surfaces after cleaning without introducing any unnatural gloss to the leather or dash materials. GREAT product, better than 303 IMHO.