I have been going to many SX races for years and yes, they DO check, but I have never had any trouble getting a camer and big lense in. I put the camera and lense at the bottom of a pack with many layers of clothing on top of it. They check, but they never dig. Worst case scenario you have to walk back to the car to put it away before you can go in. I've never seen anyone hassled for a camera once they are inside.
I went to Oakland last weekend, and I dind't take a camera (because I was taking my 6 year old to his first ever SX), but I took all the food and drinks I wanted. Just pack creatively.
07 Yamaha R6
07 KTM 950 Super Enduro
04 KTM 250exc- plated two-stroke
01 Kawasaki KE100
74 Honda MR50