"High-tech" is a vague term, though usually it refers to the addition of pressurized CO2 and ferts. You can have a low-light, high-tech tank, but that probably won't dramatically increase the nutrient demand of your plants over a low-light, low-tech setup.
Between your tap water, KNO3, and KH2PO4, you may have enough potassium, regardless of "tech" level. But it's unlikely that KSO4 will hurt in any case, so even in low-light, low-tech, you *can* add it, whether or not it's necessary. So long as you do regular water changes according to EI method, that is.