Things like 
's Hawkshot, {{summoner:2}} and 
grant vision on enemies. Can the enemy see the animations / effects too?
I'm guessing yes.
Are there any enemy reveal skills that do not tell the enemy that you can see them (besides 
and 
)?
Edit: Reworded some things to make it clearer
The enemy can see the spell/item being used, but they do not gain vision from it
Quinn says something and there is an expanding circle when she uses her vision that makes it very obvious, but I don't think you can see this if she's in the fog of war. Also, the enemy team cannot see Rek'Sai's sonar.
You can, however, see the exploding hawk and a reveal circle for those listed in your post, even when you cannot see the champions that used them.
rengar ult, he gains vision of enemies from further than they get a ! sign that he's in leap range
with the scrying orb you will see a little icon appear over the enemy's head granting you vision. they can also see that, and they see the scrying orb circle as well (so they know what you did and didnt see)
they can see the visual for hawkshot and the glitter it leaves behind as well. they don't see the exact area that it covers though.
As the other examples indicate, it works on a case-by-case basis. For example, Twitch ambushes are very dangerous because you can only see him going into stealth and he can travel a far distance in it. Abilities that specifically reveal a champion hit will usually show as a debuff though.
