Doesn't a 'safety in numbers' birthing/hatching tactic mean that some individual newborn animals are being asked to 'take one for the team'?

The alternative would be ALL of them doing that!!!!!!!!!!!!!!!

Your phrase "are being asked" makes your question difficult to answer because nature doesn't "ask" any organism to do anything.  Different kinds of organisms follow different strategies for maximizing their numbers of surviving offspring.  One strategy is to produce many offspring.  A given turtle doesn't produce a truly large number of offspring, but when many female turtles gather together on a beach, the high total number of offspring may give each female a better chance at reproducing. 

That's a bit anthropomorphic but there is a selective advantage to the synchronized hatching, as you have noted. BTW, once the turtles make it to the water, the fishes are awaiting their turn to eat them. The synchronicity is also shown in "mast years". If trees such as beech produces fruit every year, but in fewer numbers, squirrels and other mast-eaters could wipe out the population. By not producing fruit every year but all producing lots of fruit at the same time, reproduction can match or exceed the numbers needed for replacement.

That is the very reason such species have such large numbers of offspring because only a small number survive.

Not really.  No individual is asked anything.  they roll the dice and take their chances just like all the other individuals.

Sure. So?     

That is an emotive and poetic way to put it - there is no asking or intention as such - but essentially yes. If the hatching took place over a prolonged period then predators would pick off every single newborn. But when many hatch at the same time there is a limit to how fast predators can catch and eat them.