On my Radeon HD 7770 with 13.4 drivers I get the following behavior with isoline tessellation:
gl_TessLevelOuter[0] = stripCount
gl_TessLevelOuter[1] = segmentCount
This does not match the OpenGL 4.1 specification which states:
The number of segments in each strip is derived from the first outer tessellation level; the number of line strips drawn is derived from the second outer tessellation level.
I also tested 12.4 drivers, and behavior in this case matches the specification.