However, let's consider 'how' a prayer is answered in the first place for a being that is said to be 'outside of time'.
To be outside of time means, in my view, that God does not experience the passage of time, nor does he view our universe as actually time passing. Rather, these might be considered as mere illusions by 'being in time' which means that our perspective is such that we cannot see the motionless Universe as lacking motion. Events are 'happenings' but they do not 'happen' per se; an event A sits in some kind of relation R to event B (i.e., Rab : which means a and b have relation R in common).
Prayer, then, can also be considered a motionless event (or, series of events depending on how precise you wish to be with what you consider on what qualifies as an 'event'). Hence, praying in a black hole or outside of a black hole is merely another relation involving 1) God 2) a person praying, 3) black hole, 4) event horizon, 5) a certain velocity, 6) the prayer being said over a certain period of their clock time, etc. Passing over the event horizon of a black hole might change the kind of relation of events that exists (e.g., from being in near flat space to fully curved space, etc), however a relation of events still hold that describe the relation between God and the individual that is praying. I suggest that it is this relation that constitutes God's hearing a prayer and nothing to do with sending some signal (prayer) through space and to some remote destination (e.g., Heaven).
Therefore, based on this ontic way of looking at things, God 'hears' prayers even if you pass inside the event horizon. Also, this approach doesn't require Hawking radiation to make sense of it.