MOSS itself is distributed under the terms of the GNU General Public License. This means that you can use, modify, and redistribute MOSS however you like; however, if you want to distribute a modified version of MOSS, you must release your modified MOSS source code under the same license.
However, distributing MOSS along with a program that uses it is explicitly classified as ``mere aggregation'' rather than ``linking'' for licensing purposes, even if MOSS and the program are aggregated into the same executable file. This means that if you distribute commercial software in executable form with MOSS attached to the beginning of the executable, you must ensure that the source to MOSS itself is available (if you have modified it), but you do not need to distribute the source to the attached program.
Furthermore, the C library used by MOSS is based on the BSD C library, and does not contain any GPL code, so linking your application with it will not ``contaminate'' your application in any way. You only need to meet the conditions of the U.C. Berkeley and the (very similar) University of Utah copyrights under which the C library code is distributed.