We don't even know for sure if that fireball animation / fireball movement synchronization leads to any statistically significant advantage or disadvantage. And if it did, whether it could be gamed that easily or reliably.
You would still have to perform the action of inserting a quarter and then pressing start. Just holding the coin button down during boot up should not give a credit. I haven't tested this, but from my understanding of the circuit, it won't. Holding the Service Switch down, though, probably does. Try holding service + start during power up. The game might start immediately... with predictable random seed at start, and predictable fireball sync at start.
 Nope. Holding the service switch down during power up does not give an immediate credit.
[2nd edit] Only a free-play kit would allow this sort of immediate start scenario.