EENY-009/IN135: Oleander caterpillar, Syntomeida epilais Walker (Insecta: Lepidoptera: Arctiidae). This is a link to an excellent article on the Oleander Caterpillar and what it does to your Oleander, it's from the University of Florida.
However, this is the section pertaining to chemical use:
Chemical control
Application of insecticides should be considered as a last resort for this insect which, while producing unsightly damage, does not kill oleander. Bacillus thuringiensis, a microbial insecticide that is sold under various trade names, is a bacterium that kills only lepidopteran larvae. It has no toxicity toward beneficial insects.
Florida Insect Management Guide for woody ornamentals, ENY-311/IG012: Commercial Foliage and Woody Ornamental Arthropod Pest Management
I had a beautiful Oleander which I used for shade, but every year it got infested with these caterpillars so in the end I gave up and got rid of the Oleander. Hope this helps.