Despite the fact that they have several parking spots free, and not to mention several grass areas empty, they keep parking in front of the only fire hydrant that could save many building (and lives?) Is it okay to leave a note on there car politely asking them not to park there as it is against the law? And if they refuse, what number would I call?
Superficially it looks like they were negligent - sue them (they have a responsibility to ensure the access to the complex is free from obstructions depends on how long the boulder was there and what warnings they gave it was there e.g if the boulder had been there some time (say a day) they they had had plenty of time to get it removed if it had only fallen say 1 hour before you hit it then they werent negligent similarly - you say they put tape around it- what type of tape? (was it reflective?) )
Get serious. The management company is no more responsible than are you, for HITTING the boulder. Learn to watch where you are going. The obstacle was marked for safety, and you ignored the markings.
They are not responsible for you hitting a giant boulder that was clearly marked, no. You were backing through the entrance? Because your only blind spot is behind the driver's shoulder, you'd have to have been going in reverse not to see it, which seems odd since it's at the entrance, and you wouldn't be going in reverse.
The lightening would hit the metal rod, not the house, so the house wouldn't catch on fire.
Take them to small claims court. They could have put flashing lights up or reflective material to make it more visible. I think they are responsible. You may win, may not but it doesn't cost much to file in small claims court. Good luck.