Did a test on Pendragon under 1.54M with dueling code in.

Had a caster wearing cloth (0 absorbtion, no shields up).

Mixed and matched gear to move his thrust, crush, slash bonus stats around.

Made sure no stat was within 5% of any other stat. And all the magic resistance stats remained static (all above 15% by the way, some at 24%). That way I could easily identify the bonus reducing the damage. In the x(-y) formula, dividing y by x.

Result : With earth, ice, AND air elementals, melee damage in 1.54 is slash. Definitely. Magic resistance has no bearing. It's not cold damage or body damage, or a hybrid of them. Just straight slash damage and slash resistance is factored in.

When the character had 3% slash resist, the melee damage from all 3 pet types was reduced by about 3%. When he had 11% slash resist, it was about 11% or 12% (some rounding is done in the formulas apparently).