Really easy....1.) If this management area gives you written or verbal instructions that this way of "marking" is accepted and to be used, then you have no choice but to find another spot.
2.) If they don't, then hunting this area will be on a first come basis. Who's to say whoever marked this area will even be hunting the same day or choose this spot when the time comes. He may have marked 10 spots. Are you to avoid all these on because he might potentially show up there? What's to stop anyone from marking 50+ sites just to try and protect certain areas that are proven?
3.) You must beware, however, if you choose to hunt this site for the following... Some guys aren't very reasonable and he is liable to still climb the tree right next to yours hoping it pisses you off and you leave. Also, even if you don't submit to this tactic, are you willing to stare at this guy for your whole hunt? I have had this happen (slightly different, i was on my private land and this guy was on his private land. I was in the tree since 2pm and he showed up at 4:30 (dark at about 5ish). I whistled, he saw me, he still climed the tree a mere 60 yards away. We basically stared at each other the whole night, and suprise i didn't see a deer. Not because two people being close scare them away, mostly becuase he showed up when he did) Regardless, that night hunting was no fun to me.
4.) Some guys are also vindictive. I had this happen on public land. I was apparently where a guy wanted to hunt that night. He came in to my area within about 100 yards. I whistled, he saw me, and instead of walking to another spot, he walked directly to me. If i am hunting, I DON't WANT TO SHOOT THE S++T with you, especially if i don't know you from adam. After yelling up my tree and saying he hunts here from time to time, he walked about 150 yards out the ridge and paced back and forth the rest of the night. He was in the direction i expected deer to come from and he clearly wasn't hunting anymore. ugh.
Anyhow, i know i said a lot and some might not quite pertain to you original posting. However, these are all possible scenarios, some of which you can't eliminate no matter how much you plan.