What I'm worried about is the damage done to your brain by breathing in plastidip fumes.
Also, how many coats are you doing? How long does it take to make each dart? What exactly are you doing to make the dart? What blasters does it work in? How are the ranges noticeably affected? There's just not enough information in this to make a write-up in which we would want to go and get some Plasti-dip and do it.
Also know that most people now use slug stefans, which are already pretty painless. And oogoo darts are similar to this in terms of being a flat rubber head.
I'd imagine that as long as you use a mask of some sort you should be quite alright, and as far as time per dart, you could probably create a simple rack that you could use to dip the foam into an elongated container to allow more darts to be made per minute.