This page, kindly provided by Melikamp, shows that some packages in the Slackware distribution have a license that prohibits use in a commercial environment:
http://freeslack.net/
So, as long as you do not use getty-ps, amp, trn, xfractint, xminesweep or xv, you are fine. There should be no need for any of those programs - Slackware runs fine without them.
It's perfectly OK to deploy Slackware in your commercial environment and use Samba so that Windows clients can access files on the server.
Eric