I suppose it could be done. Is the beaver thick enough to form a good holster? If it's too thin or supple, you could use cowhide and then overlay the beaver as decoration.
I can remember who, but there is a company that makes a lot of cowhide holsters with various decorative overlays like stingray, rattlesnake etc. Their holsters look very nice. Google might find a few examples for you.
Good luck and let us know how it turns out.
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