If it doesn't work with an ortho camera, it isn't going to work with a tk2dCamera. It suggests the script isn't going to work properly - perhaps was written for an older version of Unity? tk2d doesn't do anything special here, you will need to find one that works with a normal unity camera for it to work with the tk2dCamera.
At the end of the day drawing lines with GL is terribly inefficient, its far better to build your own mesh and draw it, or use Vectrosity or something like that.