Yes, but the last time I used it I had a hard time getting the crickets to eat it. But that might be because I freeze it to keep it from going bad so quick.
Kale is a "sometimes" food for gut loading. There is a great series of blog posts by sandrachameleon on gut loading, including the best items to use. Do a quick search here in the forum and you'll find it.
I'd recommend buying a bag of bug buffet or cricket crack from the Chameleon Food section on here. Nick Barta sells them by the pound, and that's all you'll really need to last you several months. It's made up of all sorts of healthy ingredients and the best part is you can sprinkle them on fresh veggies to feed your feeders. It's so much more convenient and easier in my opinion.
I always thought dandelions were supposed to be the best along with grape leaves for calcium and mulberry for protein. Dandelions are still Live and growing until there's been snow for more than 3 weeks straight or below freezing temps with no break for at least a week and a half.