That's weird.
According to this thread scale do affect damage. Male Breton is 1.00, Altmer is 1.08
http://www.gamesas.com/index.php?/topic/1286166-hidden-stat-differences-based-on-race-selection/
As for the silent roll ability, perhaps only the instance of Mercer that goes with you to snow sanctum has it?
From what I have read in the thread, no one actually tested the damage over different races, all I can find is a list of assumed numbers that no one verified.
Here's my workings;
Hitting Imperial Captain with a Daedric Warhammer (first enemy you meet with a new character);
Base hp = 50
After one hit;
Breton = 44.21 (Scale 1, base 1.00)
Altmer = 44.21 (Scale 1, base 1.08)
Breton = 38.41 (Scale 2, base 2.00)
Altmet = 38.41 (Scale 2, base 2.16)
Changing scale via the console effects damage, sure, but everything in the game has a default console scale of 1 so damage wont be effected by race. Base scale doesn't effect damage which is what is different between races.
If their run speed tests are correct, then the taller races run slightly faster, which makes sense, but it doesn't effect damage.
Apologies. I have seen an NPC do an ability that resembles a Silent Roll when they were stealthing behnd me. It may not have been Mercer Fey... it was the quest with the guy who needs me to help him clear the necromancer from his family tomb. I forget his name.
http://www.uesp.net/wiki/Skyrim:Hillgrund%27s_Tomb?