The ebony will work fine as a buttplate, and can even be checkered nicely if not a PITA to do so - just don't adhere it to the stock.
IDK about oil-finishing (whatever) the ebony, though - I usually just polish the untreated wood.
I always apply stock finish to the raw stockwood in hidden areas like inletting, and under the BP & PG cap - if they're screw-attached, & not adhered.
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