I think you are ok to use the system to generate income, but you have to make sure all the links are intact. Depnding on what system you are using you may have options as far as commercial licenses. I know PHP NUKE has the option to remove copyright info for a fee. Its important to double check with the cms system you are using.
Server specs (Server OS / Apache / MySQL / PHP / DragonflyCMS):
Red Hat Linux 7.3/Apache 1.3.33 /MySQL4.0.22-standard/PHP4.3.11/CPGNuke 188.8.131.52