Would the divine realm act upon prayers even if the outcome would be harmful to those praying?

The answer here is a categorical, "No. We will not cause harm to anyone." So there are acts of omission where harm might result in our deference to ongoing events, but that is not our direct doing, it is the fault of who set those forces in motion. Our failure to stop them might be constrained through other free will considerations of the participants themselves. This is why we cannot stop crimes in progress and rescue everyone who is having an accident or injury of some kind. It is a function of whether they are partnering with us and under divine watch, whether they have prayed for the kind of support needed in the moment already, their level of belief, and belief in themselves, and whether there is a karmic liability that might be served by having them encounter a struggle of some kind or suffer to repay a karmic obligation in kind they have incurred in causing harm to someone or themselves. So there are always many considerations that need to be carefully sorted out. We have the luxury of going across time, so we can plan for something that is imminent prior to the event itself in such a way that we are ready with a response should that be appropriate, not to mention we can indeed think and act much more quickly than a human being.