Yes, as long as you give proper credits:
Marble usually uses several different sources of data to compile the map. We use only data which is "free" as in "Free Software" (which means that it's free as in "speech" not as in "beer"). Often we are using data from NASA or the CIA which is placed under the public domain according to the <a href="http://en.wikipedia.org/wiki/Freedom_of_Information_Act_(United_States)">Freedom of Information Act (FOIA)</a>. We also use data that is licensed under other free licenses which are in accordance with the Debian Free Software Guidelines (DFSG). This usually means that there are basically no "strings" attached to the data except for proper attribution. To find out about the actual licenses of the data you can have a look at the credits section for the data in Marble's About dialog.
For the OpenStreetMap map in Marble it's important that you add a line to your publication which gives credit to the OpenStreetMap Project.
This depends on which map you are using in Marble. If the bug is not in the OpenStreetMap map then you should report it to bugs.kde.org.
If the bug occurs for "OpenStreetMap" then there are two options:
1.) Please consider <a href="http://wiki.openstreetmap.org/wiki/Getting_Involved">getting involved</a> with the OpenStreetMap Project. This has the advantage that you can fix the bug yourself.
2.) If you don't feel like fixing it yourself but if you just want to report it then <a href="http://wiki.openstreetmap.org/wiki/OpenStreetBugs">OpenStreetBugs</a> might be what you're looking for.