On c3js spine graph is it possible to hide the line using the API? I know I could use a scatter graph instead, but I got to use spline with my requirements.
Also, setting the opacity of .c3-lines.c3-line to 0 is hiding it, but I want to know if I can achieve it through the API
Yes you can hide it using the API. See http://c3js.org/reference.html#api-hide. Samples from the documentation.