If anyone else is wondering--
We just got back from Knotts and the security guards didn't check our stroller or cooler, only our backpack. We did have snacks in there and he didn't say anything. I also saw him check out another lady's cooler and she had lots of food, and he didn't say anything.
So---not sure if it's up to the security guard or what. I did call guest relations two weeks before and mentioned our strict diet and she said to tell the security guards the food was for health reasons. No one even asked.