In what ways would a Professor's LinkedIn Recommendation differ from his Recommendation for Graduate School(Masters/PhD)?
In other words: In what was does the visibility of a Recommendation change a Professor's Recommendation?
I believe they are totally different.
In short: Academia:- Recommendation Letters. Industry: doesn't hurt to let your supervisor recommending you - if they do have account on LinkedIn :-)
Viewing LinkedIn recommendations may require to register and login. Just because you have a LinkedIn account, does not mean your employer has.
As a result, I would suggest to include the full text of the LinkedIn recommendation, not just a reference to it. But then it becomes not much different from just an ordinary recommendation that is just placed for public viewing on some website.