Are the seeds of the Eugenia tree toxic to animals?
I reviewed the lists from the SPCA and found no reference to toxicity of Eugenia spp for dogs, cats or horses.
But there are over 1000 species in the genus Eugenia, so it would be best if you were more specific in your identification of the tree and type of animal that you are concerned about.
I have eaten fruit of Eugenia myrtifolia, Australian Brush Cherry many times. It's sour and I wouldn't want to eat more than a few, but I experienced no sickness. If an animal were to gorge on them and eat the hard seed core, then it may develop problems that aren't necessarily toxicity.
It's always best to check with a local vet or animal welfare organization in your area.