Narcissist can play nice, if they see a payoff for themselves.
In his book, The Selfish Gene, Richard Dawkins gives examples of how altruism may just be another form of narcissism/self interest. When someone helps someone else, they may be hoping for reciprocal help. Future Benefit.
In volunteer groups and non profit associations you will find narcissists. because that is where they gather. Wherever there are people to give them narcissistic supply. I found a web site that warned of narcissists who love to do volunteer work, they get attention by appearing to be giving to others. In fact I have been in situations in non profit organizations where the people are there to get attention. In the worse case scenario, they take over, imposing their vision on the organization; it has to look good, not necessarily do anything.
Simply by looking in the newspapers at the society pages, you will see the people I am talking about. Ns want to see and to hobnob with the rich and famous. (Let's be honest, we all love to hobnob with alpha people.) Not that I am disparaging charity and non profit organizations, in fact most people do good work, but as soon as something looks important then the narcissists come running, clamoring for attention, control and victims.
In my own experience in an emergency, I saw narcissists and non-narcissists working side by side. The only difference was that when the camera crews arrived the Ns ran to be interviewed. They love the attention.
Vested self interest
We all have genes that want to pass on their information onto following generations. At least that is what
The Shakers had a philosophy of life that understood that the nature of human kind. They planted three fields of any crop, knowing that they would sell the produce of the first, keep the produce of the second for themselves and the last one would be eaten by crows and thieves. Perhaps that is a strategy with dealing with Ns, you should always have a little something to give them, but save the best for the more deserving.