Answer 1

of course it isin the generation 4 game like platinum. BUT, Darkrai is only available in nintendo event only, or you could use an action replay code if you want which is WRONG! hope this usefull...

Answer 2

You can get Darkrai in Pokemon Diamond, Pearl, and Platinum.
There is also an event for Darkrai on Pokemon Black/White
on May 9th 2012!
Hope this helps!