As demonstrated on the example of the Iron Maiden.
Usually the devotion triggers a lot and leaves clearly visible green patches behind.
On some monsters the proc never appears at all. It’s very noticeable, in both loss of visuals and DPS.
Edit: I was able to trigger the proc with other skills, but not with Vire’s Might.
I was also able to trigger other procs (e.g. Fissure) with Vire’s might on Iron Maiden.
Just not the combination of Aetherfire on Vire’s Might, and only on certain monsters.