It's "possible", but since unraveling is difficulty based, you'll stop gaining from unraveling items that are easier to get before you get to GM, much less 120.
This mostly helps those who are lower in skill, while still leaving the small chance that someone with higher skill might get an occasional 0.1 gain from unraveling an unwanted artifact for a relic fragment.
Keep in mind that the difficulty of the unravel attempt is set at 2 times the item's base total intensity. So, an item with 200 intensity will have a difficulty of 400, which translates to 40 skill. Since unraveling had a focus value of 70, you take half that, 35, and add it to 40 to get 75 skill. What that means is that you will never gain a point of imbuing skill unraveling a 200 intensity item past 75 imbuing skill.
In short, you'd need an awful lot of high intensity items to gain significant amounts of skill at higher levels via unraveling.
*Disclaimer*
This is going to be complicated and confusing to read, so stop here if you don't really, really care about how it all works under the hood
The way the skill gain system works depends on three values: your skill, the difficulty of the attempt, and the focus value of the skill. The focus value represents the "window" of skill values where it's possible to gain from the attempt, and it's centered at the difficulty of the attempt. So, in our case, the difficulty is 40, with a focus window of 70. That means that you have a chance to gain if your skill level is anywhere from 35 points below or above 40 skill (in this case, that means anywhere from 5-75 imbuing skill) Anything below that, and it's too hard, anything above that, and it's too easy.
So, to even have the tiniest chance to gain at, say, 115 imbuing skill, you'd need to unravel something with a difficulty of 80 (115-35). UO uses a 1000 scale internally for skill values, so 80 becomes 800 for the purposes of calculating the chance to gain. Since the difficulty of a given unravel attempt is double its intensity value, you'd need an item with half the difficulty value, which would be 400 intensity, to have the slightest chance at gaining a point of skill at 115 imbuing.