I recommend mapping the characters to the number row in the same order that Windows OS has it, (outlined by the Wikipedia article) because that is the standard for most Hebrew users. And using the 'Alt' key + 'Number' key to type the vowels like the Mac OS, because it seems you already have some special characters mapped with the 'Alt' key.
It seems like this would be a quick fix, so someone please work on it soon. I work at a school and this would be a big help for making chromebooks a viable tool for us in the coming school year.
It doesn't work.. When I go "language and input settings" I see the add button, and when I press it I see the possible languages... When I select Hebrew (Or any other language for that matter), and press ok, nothing happens....