Vortex Flow works with Mantaflow, an incredibly powerful FLIP fluid solver. Since Blender 2.8, this is the standard engine used for fluid simulations, so everyone has acces to it. No addons or installs required.
It also works with FLIP Fluids in Blender 2.93. At the time of writing, you will need an experimental version of FLIP Fluids, see the relevant section in the documentation.
No, although it is the first of its kind to get correct looking, animated detail on simulations, the shaders can also be used on normal meshes. Animating normal meshes can be done with a constant flow or wind direction, or a custom flow map texture.
Vortex works the best in Cycles, Eevee is partially supported. Using fluid simulation data for instance requires the Point Density node, which isn't implemented in Eevee (yet). The scattering in Vortex Water also works a lot better in a ray tracing engine like Cycles, and doesn't look as good in Eevee. Depending on the machine Eevee might suffer a performance impact from using Vortex Flow or Foam.