It can be suppressed, only appears for about 1 second or so, by adding "--nosplash" (without quotes) in "startup.properties" file. It can't be disabled entirely, unfortunately.
The splash screen file is saved in "frd.jar". You can open it with your favorite archiver tool (7-zip for example). The path is "/cz/vity/freerapid/core/resources/icons/splash.jpg". I suppose you can replace it. Make sure to backup "frd.jar" before you make any changes.