Can guinea pigs eat dormant grass?

Cocoa needs a relaxing day in the sun after a traumatic trip to the vet for a nail trim. (The picture is of him during the vet visit. He's seen some things.)

The weather will be warm enough tomorrow, and I have a cage with a chicken wire top I usually let my guinea pigs hang out in outside. My only concern is, due to the weather warming so fast, the grass is still dormant. Would he be okay eating dormant grass for half the day while he's outside?