parc rules (in French)
There's a linked PDF that says there's no camping at all unless authorized by the Park Director, but I'm guessing said authorization has been granted, since the web page says camping is OK between the hours of 19h and 9h, at a distance of one hour's hike from the park border or any road.
Note there are 42 huts ("refuges") in the park, see map. I imagine there's a fee to use them (at least during summer), certainly reservations are a good idea, and there may be a camping-exclusion zone beside each one. Contact info: http://www.ecrins-parcnational.fr/nous-contacter.html
Edit: "Massif des Ecrins" page here on SP confirms "dusk to dawn" camping is OK, says camping right beside the refuges is actually encouraged.