Very valid points. Do you know of anyone that has had issues with their monitors being kept on eucalyptus leaves? I'd be interested to hear about it. I've only had my monitors for three years, but they've been on eucalypt leaves for most of that time with no issues.
Because eucalypts drop their leaves steadily all year round, the ground in lace monitor habitat is covered in eucalypt leaf litter. The wild monitors certainly do not avoid it. When I put fresh leaf litter in my enclosure, my monitors investigate it by digging and tongue flicking, probably because I collect it from out in the bush. It probably smells of small skinks and other animals that live in the leaf litter, perhaps even other monitors.
For the most part, those leaves are toxic if ingested, but even then many animals (aside from native phasmids, koalas, greater gliders etc) can eat them with no ill effect. We used to feed them to giraffes and many other large mammals at the zoo.
Many of those toxic leaves have very good antibacterial properties when applied topically. Australian 'tea tree' oil is now a very popular naturopathic ointment for all sorts of things. It comes from a type of Melaleuca, whose leaves have a similar smell to Eucalyptus species.
I would agree with you to only use dried eucalpytus leaves (I collect my enclosure substrate as leaf litter, which is already quite dry).