I'm not sure how that's relevant. It's about the intent of the person calling the hit/making the prayer.
It's about the action, not their thoughts and desires. The action of attempting to hire a human being to kill someone, is what is the crime. A prayer to God, while an action, is on the level of wishful thinking or desires. The state would not view that as actually hiring a person to commit a murder.
Praying to God to kill someone, is not recognized in this country as a crime, anymore than sticking pins into a voodoo doll would be considered assault, even if their intention was to inflict harm via magic. It only recognizes actual potentials for actual crimes. It doesn't recognize magic or the supernatural as means to commit crimes. At least not yet while we are still not a theocracy.
In the case of Person A, even if it turned out that Person A was mistaken and the hitman didn't even exist, Person A would still have committed a crime.
I can't see how Person A would be mistaken about the person they were talking to existing. Would they arrest someone with a mental illness who was asking an imaginary person on the street to kill someone? Would pressing charges against them for attempted murder stick in a court of law? I seriously doubt that. The person was speaking to a figment of his imagination. Simply saying, "I wish they would die", is not a crime.
But that's not true.
If, say, a doctor or lawyer violated confidentiality rules in a public prayer (e.g. praying in front of their prayer circle for the welfare of their patient/client, going into more detail than allowed), they'd be liable for that.
That's because they revealed actual private information about actual people in front of actual people. But prayer for God like this, "Lord, I ask that YOU reveal the private information about my patients for me", is not revealing anything at all. It's asking God to commit the crime. Same thing in praying for God to kill someone. Nothing is going to happen. And if it did, there's no way they could link God to the crime.