Kale gets a bad rap for oxalic acid that it doesn't really deserve. Many of the plants in the same family that have good reputations as reptiles stapes actually contain more oxalates, such as collard greens. Almost all leafy greens have oxalates in them but the ratio of how much oxalic acid vs. how much calcium is an important measure, more so than just what level of oxalates.
Carrots actually bind more calcium than some of the foods you often see in the warning lists because they don't contain enough calcium in themselves and are moderately high in oxalates and so will bind up calcium from other foods eaten at the same time, resulting in a net calcium loss. Kale contains considerably more calcium than oxalic acid so while your reptile won't get full use of all the calcium in it, there is no loss of calcium leached out of other foods.
The Philadelphia Zoo uses kale as a staple in their base salad mix for herbivorous and omnivorous reptiles and their bloodwork comes out with excellent Ca:P ratios.