Morgot's servants more terrifying than Sauron's?

[Inziladun]

Originally Posted by Rhun charioteer

Wait where does it say dwarves were immune from becoming wraiths? I mean it makes sense given the whole dwarven feä but do you have a source on that?

The Dwarves indeed proved tough and had to tame; they ill endure the domination of others, and the thoughts of their hearts are hard to fathom, nor can they be turned to shadows.

The Silmarillion Of the Rings of Power and the Third Age

But [the Dwarves] were made from their beginning of a kind to resist most steadfastly any domination. Though they could be slain or broken, they could not be reduced to shadows enslaved to another will; and for the same reason their lives were not affected by any Ring; to live either longer or shorter because of it.

RoTK Appendix A III: Durin's Folk

Perhaps Aulë might have had a bit of prescience when fashioning his children?