Mosaic of Saint Uriel by James Powell and Sons
Unlike many of the “missing” Archangels, Uriel already has a well defined place and personality in the cosmology of In Nomine. You can see it in the bios of David, Michael, Lawrence, and Khalid. You can even find a good chunk of his mechanics buried in the Ethereal Players’ Guide (pgs 140 & 141).
Uriel’s Servitors were never designed to be PCs. Their attunements are significantly more powerful than most, but their dissonance condition make them especially hard to integrate into a party.
Dissonance Condition
See the Ethereal Player’s Guide pg 140.
Choir Attunements
None of Uriel’s Servitors can fall. In theory they can accumulate discords like a demon, but they’ll usually be killed first.
Serapim – See the Ethereal Player’s Guide pg 140.
Cherubim – See the Ethereal Player’s Guide pg 141.
Ofanim – Uriel’s Ofanim were creatures of pure motion, ill suited for the corporeal plane. During combat the Wheels of Purity remain capable of attack or full evasion, even if they have taken Celestial or skill based movement.
Elohim – The Elohim of Purity can look at a Celestial and automatically learn his level of dissonance as well as what Discords he has. A small number stayed with the Tsayadim, but most surrendered this attunement and joined Dominic.
Malakim – See the Ethereal Player’s Guide pg 141.
Kyriotates – Uriel only permitted his Kyriotates to possess willing hosts who had been ritually purified. However, once admitted, his Dominations could remain for months rather than days. A very small number stayed with the Tsayadim. Most joined Gabriel, Michael, or Novalis.
Mercurians – The Mercurians of Purity were charged with discrediting (or removing) human heretics and sorcerers. They can automatically tell whether or not someone is symphonically aware. Their very nature made it impossible for them to follow Uriel after he was declared a heretic. They have scattered among the various superiors, though there are large populations in service to David, Eli, Khalid, and Lawrence.
Grigori – Uriel has no Grigori, he saw to it that they were all wiped out during the flood. Prior to that they had been able to add their Celestial Forces any roll made to resist Infernal or Ethereal abilities.
Bright Lilim – Uriel does not trust Lilith or her creations. He would most likely reject any such petition out of hand. However, if he could be convinced, it would only be by someone so pure and loyal that they would join the Tsayadim in exile. These Givers may impose Binding Oaths (Celestial Player’s Guide pg 50) instead of accepting Geas Hooks.
Servitor Attunement
Divine Surgery – Divine Surgery may only be performed on a willing target. The surgeon selects one Discord. That discord is entirely removed from the target. However, the target also loses 1 Force from the corresponding realm plus an additional Force for every 3 ranks of Discord so removed.
Hunt – See Ethereal Player’s Guide pg 140.
Ripples – See Ethereal Player’s Guide pg 141.
Invocation
Chance of Invocation: None
It has been impossible to invoke Uriel since he was recalled to the Higher Heavens
Former Chance of Invocation: 2
Former Invocation Modifiers
+1 A phial of holy salt
+2 A pious virign
+3 A blessed and sanctified slaughterhouse
+4 Confronting a Pagan God
+5 Performing a purification ritual in the Ganges
+6 Confronting a Superior
Book of the Neglected 
Do you have any recommendations for weakening/strengthening Uriel? My setting features a variation of Uriel that attacks Hell instead of going after the Marches.
I don’t really think strengthening is required. His attunements are already pretty buff as is resistance to falling.
As for toning down most of the abilities can just be made less. Weeks instead of Months. Dissonance but not discord, etc.