(x11-wm/compiz-0.7.8-r1) /usr/bin/compiz-manger's running_under_whitelisted_driver(): [..] for DRV in ${WHITELIST}; do if egrep -q "Loading ${XORG_DRIVER_PATH}${DRV}_drv\.so" $LOG && ! egrep -q "Unloading ${XORG_DRIVER_PATH}${DRV}_drv\.so" $LOG; then return 0 fi done verbose "No whitelisted driver found\n" return 1 [..] XORG_DRIVER_PATH is set to "/usr/lib/xorg/modules/drivers/+". However, my $LOG file contains the string "/usr/lib64/xorg/modules/drivers//nvidia_drv.so". This is actually supposed to match, but doesn't due to the "64". I edited the file and inserted "(64)?" and compiz starts successfully. I guess I just missed something; compiz-manager has been used by a lot of people on amd64 and it would be weird if I was the first one who encountered that error.
Thanks Tobias. Should be fixed now.