Most fertilizers don't include calcium or magnesium although some do include the latter. I believe the problem is that calcium particularly would cause problems with solubility of the other nutrients so they don't mix them together. You'll usually find that a commercial potting mix would already include dolomitic limestone, which would cover both calcium and magnesium. Soils naturally contain both but in general a deficiency of those would be more likely if the soil is acidic.
I would definitely not use extra calcium (lime) on daylilies unless you absolutely know for sure that the soil is significantly acidic. Too often some daylilies have a problem with micronutrients when the pH goes above 6.5 or thereabouts. It is possible to supply calcium without affecting the pH (gypsum) but one really needs to know one needs it first.
I have a few quibbles with Dan's article but as far as I recall he does appropriately say that you need to get a soil test. Without a soil test you don't know what nutrients you already have in adequate supply and therefore what might be low, or too high already. You can then end up oversupplying a nutrient which can cause a deficiency of another - or just fail to provide enough of something that is lacking or tied up.
If you're concerned about rust you need to be careful not to go too high with the N, and you need adequate potassium. If short scapes may be indicating low K then that could also be impacting rust severity.
