Looks like no one is going to legitimately answer the question of "Has it ever rained at a coachella valley music festival"
It's raining right now.
It's been raining and will continue to rain for some time.
Keep in mind that '"Coachella" is technically in Indio.
It's also safe to say that it's raining both in Coachella, Indio
and the site where the 2010 Coachella Music and Arts Festival will be held.
Than said and in an effort to legitimately answer brifloras question, no.
To the original question, yes.