You pretty much can't use the unity animator for c# properties just variables. It has been an issue since it was introduced but still isn't resolved. The animator only works for variables, and to get that to work with tk2d would mean sacrificing a whole load of performance. I have posted a few adapter class examples on the forum which will make it work better trading off performance. tk2d works best with a script controller.
About a waterfall - it depends on the size, if its a large image, just create a looping animator that plays on start. Dicing could help reduce atlas sizes, but trades of a little bit of performance. Should be fine if there is only one waterfall though.