UN related services are now using cryptocurrencies, interesting. I would prefer if they put solar panels in Australia and mine cryptocurrencies with it rather than using coinhive.
They choose to follow the easiest way to make a few bucks without people feeling that they lose anything of monetary value. I don't think they will ever try to actually set up solar based rigs or mini farms for that purpose.
It's too much effort and would require them to hire people to keep monitoring everything, which costs money too aside from all the hardware. Why doing that when you can just sit back and see money come in like this?
I honestly wouldn't even want a charity to actually start getting involved in mining. The main incentive is to raise gifts and income from selling merchandise. The more they earn, the more goes to top board members.
These charities spend more money on marketing and their board members than the actual purposes they raise money for.