I think this is a great idea. Instead of donations going toward arming the troops, this is something that provides emotional and economic support. Neat idea, regardless of whether you approve of the beneficiaries of the charity.
No, I don't think there's an equivalent service that allows donators to send pizzas to Palestinian fighters. Go ahead and set one up, they could probably use it. Make sure it's Sbarro pizza -- for that extra moral resonance.