I have used 3 species of gum leaves which look like yours Eucalyptus tereticornis, Eucalyptus Cedar, and Eucalyptus globules, as well as Eucalyptus robusta, and Eucalyptus torelliana which have different looking leaves. But none of those have the same shape are as big as what you're showing in the pictures, their leaves are 3 - 4 inches long on average.
Apart from the leaves and flowers, the trunk is also an important clue. But as I said, check out local websites, or other info to figure out what gum trees grow in that area first, and narrow it down from there.
I ask about the smell since if it does smell like lemon, it could be Eucalyptus citriodora and it is definitely NOT SAFE.
My rhino roaches actually prefer Eucalyptus globules, and grass hay (for feeding turtle stuff) over any other leaves, mulch and actually, anything.