Feeder insects usually have a poor ratio of calcium to phosphorous, so dusting them with a phos.-free calcium powder helps to make up for this. For my veileds I dust with this at most feedings.
I dust with a vitamin powder that has a beta carotene source of vitamin A twice a month. Vitamin A from beta carotene sources can not build up in the system, but those from preformed sources can. However, there is controversy about whether all chameleons can convert beta carotene into vitamin A, so it may be necessary to provide a little preformed from time to time. Excess preformed vitamin A can build up in the system and prevent the D3 from doing its job...and lead to MBD.
Because my chameleons usually only get UVB from artificial light, I dust lightly with a phos.-free calcium/D3 powder. Excess D3 from SUPPLEMENTS can also build up in the system and lead to problems....but not enough will mean that not enough calcium can be absorbed...so you need to reach a balance. If a chameleon gets its UVB from direct sunlight, then it won't likely be necessary to give it any D3 supplement.
Appropriate basking temperatures are important for good digestion which plays a part in nutrient absorption.
Phosphorous, calcium, D3 and vitamin A are four of the big players in bone health (and they play other parts in the body too)...so they must be kept in balance. Its important to look not only at what the insects contain, but at what supplements you are using and what you feed to the insects and gutload them with.
Keeping them the way I do, my female veileds usually live to 6+ years of age and the males live even longer.
As far as feeding them fruit goes...I give mine a little with the greens and veggies and it hasn't seemed to cause any problems.