I was wondering assuming you have the "Light Armor Use" skill, is it better to make use of this skill and use a leather shield with armor P/B/S/M/E of say 5/5/5/5/5 or are you better using say a dragonscale or metal shield with higher stats of say 10/10/10/10/10 assuming they are the same weight in regards to armor deflection?

I would say use the leather one as to make use of the light armor skill. So basically you have a chance to both shield block and deflect.

With a metal shield you will only put the shield block skill to use.

You can incidentally use skills you don't have. It happens all the time. Same goes for dual wield, parry, dodge, etc. The chance is low, but it's still there.

Armor use skill boosts the effective AC for deflection purposes. An armor with much higher AC would still be better, but I've no idea how much higher it has to be to offset the lack of skill.