journaling generally interferes with dump(8). It seems odd that they would be using dump to do backups though, since they are virtualizing the OS.
The parent link to gjournal is weird too, since gjournal is not the same as softupdates w/journaling (SU+J). It makes me wonder if they actually disabled softupdates too.
I found a random post[1] about issues (unmapped io?) running i386 freebsd with su+j in virtualbox (apparently a virtualbox bug[2]).