Encapsulated stains are made by special processes that 'coat' the individual particles (i.e. cadmium) with silica or zirconium. In this way they can be suspended in a melt with minimal dissolution of the harmful metals into the glass. These stains are very expensive, must be used in larger amounts, and come with lengthy safety data sheets and must be used according to instructions.
How to include stains in chemistry calculations in Insight
The simple answer is that you should not. The chemistry of stains is proprietary. Stain particles do not dissolve into the glaze melt like other materials, they suspend in the transparent glass to color it. That is why stains are color stable and dependable. In addition, their percentage in the recipe, not the formula, is the predictor of their effect on the fired glaze. Of course they do impose effects on the thermal expansion, melt fluidity, etc., but these must be rationalized by experience and testing. But you can still enter stains into Insight recipes. Consider adding the stains you use to your private materials database (for costing purposes for example).