Using the images of your employees (especially CANDID photos) in advertisements IS commercial use. Unless your employees signed some kind of legal release that allows the employer to use them in this manner, I would check with your company's legal counsel for guidance.
Pictures - 2011 I was released on: USA: June 2011
Wasn't Planning on It - 2011 was released on: USA: November 2011
Hopeless Pictures - 2005 was released on: USA: 2005
Talk About Pictures - 1978 was released on: USA: 1978
Atop the Fourth Wall - 2008 Comic Book Advertisements 4-30 was released on: USA: 25 July 2011
Planning the Heist - 2013 was released on: USA: 1 June 2013
Cooking Planning and Organization - 1948 was released on: USA: 1948
Pictures - 2011 II was released on: USA: May 2011
Living Pictures - 1899 was released on: USA: May 1899
Clear Pictures - 1994 was released on: USA: March 1994
Pictures at an Exhibition - 1973 was released on: USA: March 1973
Your photographer owns rights to any pictures he/she has taken, unless you get a signed release. Most photographers charge a flat fee for both the release and a digital copy of pictures. Be sure to ask if you will get all of the pictures, or only the ones the photographer thinks are best.