A post from Reddit:
http://www.reddit.com/r/DestinyTheGame/comments/2gr68k/while_farming_the_cave_of_treasure_in_russia/

Since a lot of people know about that spot it's usually crowded when I get there. So last night I did a few tests just to see how much the other people around affected the loot that I was getting.

Disclaimer: what I'm about to post may already be common knowledge, but I just figured it out and haven't seen much discussion on it. So please don't down vote if you already know.

When I got to the cave there were 5 people already farming it. A fireteam of 3, fireteam of 2 and me playing solo. For the first 10-15 mins I was blasting the mouth of the cave just like everyone else and I wasn't getting a lot of kills but loot was still falling (mostly greens and a couple blues). Then I decided to just watch the cave with my sniper scope. My theory was that maybe I don't have to be the shooter, just "witness" the kill. And that worked. I still got loot.

The other test I did right before I left was to see if just being in proximity to the 5 other people, but not watching the cave would drop loot. I crouched behind the slanted rock in the back and was looking 90 degrees away from the cave, I did not witness any kills. And when we all ran in to collect loot / ammo I picked up 2 engrams, they were legendary but I don't think this gives you a higher chance for purple. They were simply the first legendary ones to EVER drop for me.

TL;DR - as long as people are around getting kills you will have the same chance to get a drop, even if you aren't shooting or a witness to the kills.

Also my grimoire kills for area and enemies still increased even though I wasn't shooting.

https://imgur.com/a/1ExnL

Apparently, another Cave of Wonders like place on Venus.