This interview with Marcy Massura offers quite an open and honest view about the role of communications within employee advocacy.  WHilst she doesn't actually answer the question asked in the title, she alludes to the fact that internal communications is an extremely undervalued part of the organisation.  One that could very quickly and easily contribute an awful lot to the organisation if they just partnered up for success.

We know from our relationships with customers that communications is centrally driven, top down using a variety of tactics.

An advocacy approach to communication encourages 1-2-1, peer-to-peer and direct to leadership.  The barriers are dropped and the transparency begins.   Communicators become the facilitators of cultural change where people from across offices and countries connect with each other and talk.

I believe that internal communications has the power to change the way they're perceived within business.  They can now attribute true value to the bottom line through measuring advocacy impact.  

So, my answer to the question...they should be!