here's an uncomprehensive list of fruits and veggies they like to eat:
Avocado, banana, strawberry, blueberry, raspberry, cucumber, carrot, corn, apples, oranges, bell peppers, mango, watermelon... There's more, of course, but this is a good list off the top of my head.
Was he damp when you had him out? He could have been cleaned/cleaning and was just wet and spiky. But if he's been like this for longer than just one night let me know.
Dog stress could be very real. Do the dogs go into the room that their cage is in? Keep the gliders in the sleeve or pocket or tightened hood of your hoodie if you can. If they trust you, they'll want to be with the warmth and smell of your body. I've found it can help de-stress a glider if something's going on. But it only works if they trust you well.
Is he hydrating? You can give him some water with a bit of apple juice in it.