It won't count as destroyed, removed, or replaced for effects that scale off the number of Beasts that leave the board, like A Dreadful Tide of Scurrying Flesh or Pent-Up Calamity. Tags: Destroy, Remove, Replace, Unearth a Beast of Wrathful Stone, 12 more...
Can Bringer of Dreams and Nightmares do real damage (destroying cities, etc) with Power X?
The answer, in general, is 'no'. If the Power says "damage" or "destroy", it doesn't matter if it also says that Dahan, Beasts, Invaders, or anything else are doing that damage, the source is still ultimately Bringer of Dreams and Nightmares and is only nightmare damage.
This applies even if the power has some other spirit doing something (eg, Blazing Renewal). If Bringer of Dreams and Nightmares played the power, it cannot do real damage.