The developer will understand the glyph and diacritics needs of the content and help plan for a font that covers those needs in all formats. (epubsecrets.com)
The Kindle does support all of the other Greek characters, including all of the pre-composed characters with diacritics... and I mean all of them. (kindleformatting.com)
If you need to type a letter with an accent mark or some other diacritic, in certain apps, you can hold down the associated letter, and a list of options will appear. (entrepreneur.com)