oggCat might occasionaly block for user input, for example when output file already exists it will ask if you want to overwrite. Also note that oggCat output progress information on standard error, not standard output. And your program might not be executing via shell but directly, in which case '> /dev/null' won't work. Try to run it via:
sh -c 'oggCat -x bla.ogg 1*ogg < /dev/null > /dev/null 2>&1' which should work around all the problems above. If it still doesn't work for you, you should find a process PID in ps output, and execute:
strace -ff -tt -p PID to find out what program is doing (replace PID with PID of oggCat process)