It's a good idea, but the dart is not a bullet: its a projectile, like the knife. You must lead the target, and SNIPING with a projectile is pretty hard, you gotta lead the target like 7 meters afar, and the target may turn around or something.
The dart is a bullet as far as the game and lua is concerned. Try playing before you assume problems. :D
We were going to implement a similar item, yet are focussing on redeveloping our VIP system atm. I would get rid of the health station poisoning and instead have it so the health station actually cures you.
Good luck with your VIP system. Are you using Evolve? Good idea, the health station poisoning is rarely used because of the obvious green colour it goes, but I think we'll keep it in for now. Also, I don't think the health station curing you is a good idea, I love the gameplay and panic created when people are being kept alive on a health station. The atmosphere steps up a notch as soon as someone is poisoned.