This article states that they do not encrypt their group chats with E2E encryption. So they might be able to.
But it is 2,5 years old, so I am not sure about the accuracy.
https://stealthoptional.com/news/is-snapchat-encrypted-how-secure-is-snapchat-messaging/
Only prepare one chest and film it being burried three times.
That way you are only out $1000 and they'll keep searching for the other 2 (non existent) chests if/when they find the chest.