There are different hardnesses of aluminium alloy, some of them fairly soft. Apparently you want to look for T6 temper aluminium alloy which gives it greater hardness.
Some Danelectros have had aluminium nuts.
The main thing you may find is that the open string sound is noticeably different to the fretted string sound, whereas bone is generally acknowledged to give an almost identical sound. But it's just a nut, and you can easily swap it out if you wish.