I tried to use it on a Misery weapon, and it didn't work. Says it's only for gear eligible for awakening. Is that normal? @Spacecats @Halrath , anyone?

Yes, the scrolls only work for awakenable gear (visionmaker) up to tier 11, so Ambush is as high as it will enchant. Items like these are really tricky because they are all coded by Bluehole to work in a very specific way. Changing them on our end to enchant other items for an event like this isn't possible.