Well... the Passions actively fought the Horrors during the last Scourge (some went mad over that, some died...), but if they are around this time to help metahumanity again is unknown.
In the base Earthdawn setting (Barsaive) none of the Passions fought the Horrors. Three of the twelve for Barsaive went mad (and there are, of course, theories as to why) but the bulk of them are ok.
In another province of the Theran empire, Vasgothia, the Passions there actively fought the Horrors with their worshippers. And were torn to bits as a result. In the forests there, one can stumble across such "Fruit of the Passions" every so often. Eating one (yuck) gives the character some pretty interesting powers. Quite variable, however, so one never knows what one will get.
There are also "Fruits of the Horrors" scattered about. These are pieces of major Horrors (god-like in power, comparable to great dragons or even stronger) that were slain by the Passions and their followers. Eating one of those...well, do I need to go into details? The problem is that the two "Fruits" look exactly alike. Good luck with that...
The overall mana level is what allows the Horrors to enter the world. However, when the mana in a specific location has been drastically altered/increased (such as the spike point from the Great Ghost Dance) then it can create a narrow tunnel or bridge between the worlds to allow some of the Horros to enter early. The big ones can't spread out far from the spike; they need the higher mana level just to exist within our world. Some of the minor ones can still cause damage, but without sufficient numbers, the threat would be contained to a limited region.
The problem there, of course, is that the major Horrors will be doing all the can to increase the ambient mana level in the area surrounding the spike. Once you give them a toe hold, the only thing I can think of that would stop them would be a nuke. And due to the second major use of the Great Ghost Dance in 2049-50, nuclear weapons are problematic (see what happened in Chicago for more information).