Can /Library/Audio/ be safely deleted?
When you say "safely", I'm assuming you mean whether it can be deleted if you are not using Garageband, Logic, or any other DAW or audio software on your Mac. The answer is essentially yes. Even if you do use this software, the folder can be 'safely' deleted, as in it won't cause ill effects in the system - but naturally some functionality of the above apps may be impaire. If you were to open/run the Apple apps above, they'd likely just recreate the folder as needed.

Deleting the folder will not affect your Mac's ability to play audio normally, such as alert sounds, music/audio on websites (YouTube and the like). It won't affect your Mac's stability or anything unexpected like that. While it appears to have a folder for 'Alerts', the actual alert sounds used by macOS are stored elsewhere.

This is one of the beautiful things about the logical, human-readable way that so much of macOS is laid out. You can go ahead and delete the folder without worry, but I might ask why you want to remove the folder? Personally, I would err on the side of caution and clear the contents of the folder, but leave the empty 'Audio' folder there, as a placeholder if nothing else.