Bish don't need help with ENY, for some reson, their ENY never gets below 12, rarely have I seen it lower (I then to check rarely as well, only when they have a large numerical advantage). At least this helps somewhat with stoping there hoards. 
No it doesn't, have you really seen the horde stopped because of eny? I have not, the times when I see the horde defeated, not quite rare-but uncommon, is when a good defense is mounted, not because they weren't in uber rides. It is rather because they were confronted with a fair defense.
Much more often than not, when the eny is high for the horde, they just bring more players...If they find a decent defense mounted at one base, they start over somewhere else. I don't see how eny affects them much, most of them fly bomb trucks anyways, and leave it up to uber players like Ahiru to kill all the defense.