The shrimps survive in the water they come in with, it can't be too bad, to me anyway. I don't try to do all the extras to get to 99% (it can never be 100%, you do want the shrimps in the tank, right?).
I cut the bag and have the water, shrimps and all into a small breeder box, turn the air flow to minimum (get like a drop every few seconds), then come back a few hours later to pour the whole thing in (sans the dirty stuff on the bottom). If I want to be safer, I might adjust the water flow to highest after a few hours and let that run for a few more hours, or even a day (yeah, sometimes I forget ;-)
Adding some ammonia or no2 (from the bag) into a tank should not affect much, as long as your tank is well cycled. Chances of having hydras or planarias hitchhike is pretty small considering the water is normally taken from the top of the tank. Bacteria will be mostly on/in the shrimps.
Lets just say all the nematodes, copepods, scuds, seed shrimp, etc have come from my shrimp orders.
I lazily poured everything in during when I first started and boy oh boy I still have the tank that's infested with everything.
The pests usually come from the plants that are put into the bag for the shrimps to hold on to.
I wouldn't recommend pouring everything in the bag. Copepods and other micro organisms are tiny and you only need just one. I would net the shrimp and move them over....my infection rate has been nearly eliminated after doing this.
Bottom line for best survivability: drip method IME.
Take some time to acclimate slowly, it'll pay off in the long run.