There are hazardous materials in concrete and mortar such as calcium oxide which is corrosive to human tissue. There are also trace amounts of crystalline silica which is abrasive to the skin and can damage the lungs.
Before mixing lime with cement, you need to make sure the hydrated lime has been completely wetted out or it will continue to absorb moisture.
Yes, hydrated lime is designed for use on lawns, gardens, and potted plants.
Incorporating an appropriate amount of hydrated lime into a cement-based mixture will make it more plasticity and improve the workability, making the product easier to handle on a trowel.