I've never had them successfully breed in my viv. Though I do let the uneaten crickets stay in the viv. Possibly they get eaten before there is a male and female that reach breeding age.
I've thought about this too. However I don't think it's a good plan to try to breed them in the viv. Crickets just don't produce an egg or two. During their breeding life cycle, a single pair can produce hundreds of eggs in a few days. This would quickly overwhelm the viv and produce a habitat fouled with their excrement and most live plant would eventually be destroyed as they'll feed on them. There just wouldn't be enough "nature" in the viv to let things occur in there as they do in the wild.