When I was involved with Dash(Darkcoin), most masternodes were hosted on Amazon and in the hot wallets. Its up for speculation though, he made it seem as if cold wallets was where coins are only stored, which isnt true.
When was that?
Things have moved on, pretty much everyone you see commenting on the community threads are doing cold wallets.
I'm sure there are some hot wallets still, but with strong encryption keys I'd wager.