Upon closer inspection of the 1h perk tree i see skills that improve Axes, Hammers and Swords.

So can I presume that Daggers are counted as Swords by this games mechanics?
'cause the only other skill I found that actually improves daggers is the Assassin's Blade perk in Stealth.

The sole purpose of daggers is the sneak attack bonus. I don't think that the sword perk changes damage with daggers.

But if you use daggers, your 1H skill increases.

One hand skill probably determines dagger dmg in the same way that it determines werewolf attack damage, and presumably by that standard regular hand to hand damage.
Personally, I'm not a fan if this is the case. Hand to hand skills and one handed weapon skills are not synonymous.

Currently still using sword and shield but I'm investing in Sneak so I can get the perk that gives you a 12x sneak attack damage bonus when you use a dagger. When I get that it's daggertime

Thats what I noticed too, thats why this question has come up