Yes, if you get it wet enough. A few quickly wiped off sprinkles won't hurt it, but depending on the leather and the color of the leather, you could end up with a bag that looks like it has a bad case of the pox.
I've been known to keep plastic bags tucked in the bottoms of my good leather bags in case of rain. I've stuffed my 2K bags in a grocery store plastic bag more than once because of sudden down pours. I'd rather look like a bag lady than ruin a good bag. This is why the leather bags are so awesome when rain is a given. No worries and no plastic bags required.
That is a good idea. I am placing an eco-friendly bag in my handbag as soon as I get off the computer. I have a very nice green leather prada and I would kill over if it were damaged by rain. I also have a nylon one which I absolutely love