What kind of output do you see in your boot.log? That file shouldn't be written to after the log4j framework takes over, and stuff starts being written to server.log.
If you are running dcm4chee as a service/daemon, can you ensure that you have this line commented out in your jboss-log4j.xml?
<appender-ref ref="CONSOLE"/>
to comment it out:
<!-- <appender-ref ref="CONSOLE"/> -->
If you're running as a service and that line is not commented out, a copy of all log messages will go to sysout and this could cause some log file growth (but usually syslog type logs).
Anyway, what is going into boot.log? Is it an exact replica of what is being written to server.log?
-- Damien