There's probably a way to put a digraph in my title, but I'll assume you know what I mean. Do people really say it as a digraph (so the first syllable woud rhyme with "cat")?
In Latin, the digraph
æ was pronounced as a diphthong, /ai/. In Vulgar Latin the diphthong smoothed to /?
, which became /i:/ after the Great Vowel Shift in English. The Germanic letter (not digraph)
æ was pronounced like the vowel in
cat. A digraph is just a way to write two letters as one, so it doesn't really make sense to say that people say it as a digraph.
Daemon is just a variant spelling of
demon, just as
haemophiliac is a variant of
hemophiliac. I'm guessing it comes from Britain, because they like to hang on to those Latin
ae and
oe spellings where Americans simplify them to
e.