It took me like an entire minute to realize what you meant by the Rasta greeting part.
I'd assume it means that
Eamonn sounds like "'Ey, Mon," which is how "Hey, Man," would sound with a Rastafarian/Jamaican accent.
I've never thought of that and the emphasis on the syllables is different enough that it's not at all a concern. Not that I'd use
Eamonn in real life anyway, so I don't even have to worry about it.