The Sorcerer feature Dragon Soul allows you to pierce resistances of which you are resistant. I have a lightning resistance. Do I also pierce Resist All when I attack with lightning spells?
All of the Sorcerers features that allow the mechanic you describe say something along the lines of:
Your arcane powers ignore any target's resistance to that damage type up to the value of your resistance. (Emphasis mine)
So in your case, you would only ignore lightening resistance up to your lightening resistance amount. Untyped resistances would be unaffected this feature.