Sorry for the very late reply, I only just saw this thread.
In case you're still wondering, it is possible to use American miles for LATAM flights, but you won't be able to book online.
You would need to use the British Airways website to check for award availability. Then, if a seat is available, you should be able to book it by calling American Airlines.
So if I check the AA site for Qantas SYD to Santiago, BA for Santiago to Sao Paulo I will be able to combine the two to book?
Thanks for your reply, it was very helpful.
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