I am talking about the ones that cause critical damage. Do they work for daggers?

Not all perks/effect for 1hand work with daggers.

I know I have decapitate some people with daggers.
I think I ve made criticals with daggers.
I know that gear with +XX% 1HE damage doesnt increase dagger damage.

Decaps definitely do work, IIRC it's only the damage output perks/enchants that don't work.

If you want higher dam, get your smithing up. Smith those svckers.

So the armsman (0-5) perks don't increase dagger damage?

I think they do (must be confirmed)
However, the +1HE damage from enchant in gear doest not work.

Are you sure about the crits?

not 100% sure (hence me saying "I think" instead of "I know" )