As far as included things under other open source licenses, basically you are trusting my judgment that only things with a license compatible with our main license are used, I am very careful about this and only use software components that are under compatible licenses but again I am not a lawyer.
The only things included in mojoPortal that have a different kind of license is the skins, some of which designs are licensed under Creative Commons Attribution license from the designer and they often require you to keep the design by link or contact them to pay for a different license that allows you to remove it. But the skins are not really part of the software per se, we ship them with mojoPortal but they could be left out, some of them have no such restrictions and you can always make your own custom design rather than be concerned with the designer license.
So you are not required for example to keep the "powered by mojoPortal" link, but in some cases you are required to keep the "design by..." link or contact the designer to get permission to remove it.
Hope it helps,
Joe