I main Kat, and first I want to tell that Ult is very good for killing Teemo. I mean, we all here love killing Teemo, right? ^_^ So it shouldn't be nerfed, it must stay as is, even if it would be unique ability. But the ability is not unique, and actually it's not rare. Some players already mention Morgana, that is not quite correct, because Morgana ult is reveal the target, rather just detect his presence.
For more examples check out http://leagueoflegends.wikia.com/wiki/Stealth chapter "Presence detection without reveal"
So, there is a small quote
All abilities that do not require single target to cast can affect stealthed champions (but will not reveal them).
Certain abilities can only be cast if an enemy is in range of the AoE casting circle - these abilities will light up and become available to use even if the only enemy in range is a stealthed enemy.
Evelynn's Hate Spike
Katarina's Death Lotus
Kennen's Electrical Surge can detect stealthed champions due to the particle effect pointing in their direction. The stealthed champion will not be revealed.
Nocturne's Duskbringer will provide semi-reveal if it lands. Though stealthed unit will still be immune to auto attacks and targeted spells, Duskbringer's trail will compromise the position of said unit for 5 seconds, even through movement.
Rek'Sai's Tremor Senses will perceive the position of any moving unit, even stealthed ones.
Soraka's Starcall heal animation shows if the skillshot hit a champion, whether it's invisible or not.
Talon's Noxian Diplomacy causes struck enemies to leave behind a trail of blood even during stealth, similarly to Nocturne's aforementioned Duskbringer.
Teemo's Noxious Trap will explode but not reveal stealthed champions.
Tryndamere's Mocking Shout
Viktor's Chaos Chaos Storm will follow a stealthed target and fire it's lightning bolts at it. The stealthed champion will not be revealed.
Vladimir's Tides of Blood can detect stealthed champions due to the particle effect flying in their direction. The stealthed champion will not be revealed.
Warwick's Blood Scent does not reveal stealthed champions but if they are within range and below half health, he will receive the movement speed bonus.