If the drive is in RW mode and is not unmounted cleanly, the ext2fs driver will force a filesystem check on the next boot, which can take a considerable amount of time. Considering that no data is really going to be written to that filesystem, it probably won't actually get corrupted, but it's possible nonetheless.

Having the filesystem mounted RO will definitely prevent a forced check and corruption.

Maybe someone could get ext3 support into Hijack. This should allow you to mount RW without fear of corruption or forced checking, even though you might lose data that is being written.