So some players told me that it doesn't count. I faintly recall that being the case from past events. I always get confused by this, because the last chest behaves diamond-ish...
- it has the same artwork as the diamond chest in Summoning Circle
- it can provide heroes whose source is reported as 'Diamond Chests' only
I might consider running crucible again if it would count towards the jade event, because it would slightly reduce the pressure on gems when trying to obtain a hero from the event.