Nih,
There is nothing particularly "special" about the armor that Umbra wears, other than the fact that she wears Ebony armor, which doesn't typically "drop" until your character is at a higher level.
What is however, special about defeating Umbra is the sword that she carries. It is argueably one of most powerful weapons in the game from a sheer base attack value. --Granted, it does not have any additional enchantments to raise/add to its attack strength, (say for example: Fire Damage, Frost Damage, Electrical Damage, Damage Health Enchantments etc) But with that in mind, the pound for pound base attack value of the weapon is (from what I've heard and from my limited experience thus far at my low level) one of the strongest, if not
the strongest weapon in the game.
To answer the second part of your question. The Umbra sword is not a leveled weapon in the sense that its attack strength is determined at the time that you acquire it. This particular weapon differs from alot of the weapons in the equipment database, in the sense that it has 1 instance. There is only one version of the weapon in the game. With that in mind, its attack strength is based on a number of things. As I understand it, the primary contributers to the attack strength of this and other Blade weapons are: Your Blade Skill, Your Strength, and Your Armourer Rating (i.e. repairing it above 100% health)
To clarify, I acquired this weapon as a level 6 Mage. (I decided to acquire it outright as opposed to acquiring it as part of the Clavicus Vile Daedric Shrine Quest) At the time that I acquired it, the weapon had a base attack value of 9. I have now sloooowly leveled my level 6 Mage character to level 15 and the base attack value of the weapon has more than doubled. I've heard of higher level characters getting the base attack value of this weapon as high as the low to mid 30's. Now if I compare this weapon to any other weapon in my inventory, (and you can verify this yourself) it has almost twice the base attack value of any other weapon that I have picked up.
The only drawback to this weapon as I see it, is the fact that it feels like a "weapon charging/depleting treadmill" in the sense that for every time I use it to soul trap a soul (or whether I use it just for its sheer power), I have to recharge it. So, it almost defeats the purpose of the soul trap enchantment. Using the sword depletes its charge. To recharge the sword you need to use it. See where I'm going with this?
But, other than that, its an excellent weapon that should probably be in everyone's inventory. And since I never completed the Clavicus Vile Quest, its still considered a Quest Item and has no weight associated with it which is a definate bonus!!