Bartender Geek

When used by itself as a title or job description, then indeed Caesar, as you say, is spelled with an yud and pronounced accordingly with a long 'ay' vowel - Kaysarr. BUT when used in conjunction with specific names, especially Nero and Julius ("Yoo-le-oos"), it is often spelled without the yud and pronounced Kessarr, with an 'eh' segol vowel, so this would fit.

xiphias, I have no idea why you say that in modern Hebrew the ayin is mostly silent. While not quite as strong as the Yemenite guttural, it is still definitely present. Don't forget that about half of all Israelis are Sephardi, who did retain the proper atin to varying degrees.