I have tried to find the answer to this question elsewhere, but unfortunately all the guides I have read so far have been rather vague on this point.

My guild is going to attempt the Twin Emperors soon, so we have been busy reading guides. What was mentioned in several of those guides was that each emperor would "punish" the reaid if it got dealt the wrong type of damage, i.e. Magic Damage on Vek'nilash or Weapon damage on Vek'lor. However I have not found any specifics on this topic.

Now weapon damage on Vek'lor is probably not a big issue anyways, as noone should be in his melee range, but magic damage on Vek'nilash can come up especially for a rogue, most notably in the weapon proc of the Perdition's Blade. Therefore I was wondering if anyone of you could give me more details on this.

How exactly does this "punishment" look like?
Is it safe to use weapons like Perdition's Blade on Vek'nilash?

Argh.

Yes.

Vek'lor will Burst when people are in melee range.
Vek'nilash will Strike whenever he feels like it.