Not sure if it's too late to inform you, you might have already been to the desert and returned.
I'm not to sure about the species you will find in the Grampians, although antaresia certainly named a few of them. You will find an amazing variety of skink species anywhere in NW Victoria, so make sure you have a decent field guide!
Some of the species I have personally encountered in and around the Little Desert include stumpies, blind snakes, marbled geckos, thick tails, brown snakes, mitchell's short tailed snakes, burtons legless, olive legless, southern legless lizard, eastern and central bearded dragons. A western brown was once found dead on the road, but that was in the range of the big desert.
I haven't personally encountered but I have a friend who has some fantastic photo's of bardicks.
To find the largest range of animals, its best to go spot lighting on a warm humid night, moonless night. Cloud cover will do. When I say warm, I mean the day has been nice and hot, so the ground/rocks still retain heat. And in terms of humidity, a light shower is always good, anything more often turns the road to sludge. :evil:
Hope that helps.