The Wiki may have led me wrong, but based on what it says I should be getting treasure caskets of one kind or another 10% of the time when fighting enemies in West Sarutabaruta. I'm relatively new to the game, so is there anything that might be preventing them from appearing?

Treasure Caskets were added way after the time period this server is set in. If you are browsing the FFXI wiki, try looking at the date the page was created on, if its after 2008 chances are it isnt here on nasomi.

Gotcha, thanks a lot!