I don't bother adding anything to the salads. I just try to offer as much variety as I can. Salads themselves are quite nutritious and can provide a really great diet on their own. The supplements are more for the deficiencies that common feeder bugs have to make up for the calcium and vitamins they'd get from a wild diet. If you want to increase the calcium content of your salads, I suggest using plenty of collard greens.
No , I used to when I started off keeping my BTS and then got Rex and Puff, it was going onto the crickets and greens and veg/pellets mix.
I found out this might lead to overdosing with calcium and vitamins so I stopped, it's just a LIGHT dusting on the crickets , and I add the residue dust to the bran the mealworms and superworms are in (so they get it mixed with the bran, carrots and greens/whites).