I'm curious... My friend got a shiny Darkrai from some random user, and I'm wondering if it's real or hacked. It's from France, is an event Pokemon (2011HVR), and has an OT of 11011. It says it came from Unova. EDIT: This Darkrai is from Gen 5 and is now in a copy of Pokemon X.
Yes, this is possible. Obviously this is no guarantee it is legitimate but it's impossible to prove it's fake from the information you've given. That said, it is unlikely someone would give away a shiny event legend to a random person.
The 2011 Winter Darkrai was released in France. It was available for generation V in Unova and does have an ID of 11011. Because it was released as an encounter and isn't shiny locked (as far as I know) it can potentially be shiny.
According to the Generation 5 Wondercard Map, offset 0x37 determines if it can be shiny.
Checking the 2011 French Darkrai here, you can see that 0x37 is 0. This means that pokemon will NEVER be shiny.
Edit: To get a shiny Darkrai, you must have gotten the encounter from generation 4 and transferred it to gen 5.