An easy and sure way to know whether the eucalypts have nectar is to observe bird activity rather than bee activity. The Marris on my property are in flower and full of bees, but they are mostly gathering pollen.
Once they have nectar in a few days time, the honey eaters like the Brown and Singing Honeyeater and Red Wattlebirds move in and can be seen feeding on the flowers. Then I know there is nectar.