That's a good question.
The On Nom ability says "all def dice are removed".
It does not say "all active and locked dice are removed".
So what I'd guess is the following:
- Normal defence dice in active slots are definitely removed.
- Normal defence dice in locked slots (i.e. due to Picket's Innate+1) should probably also be removed.
- Skill dice (including constant defence) are not removed.
- Any bones in the backup plan that come from defence dice are not removed. While a die is in the backup plan, it is a bone in the backup plan, not an attack/defence.
George nailed it, great answer!