I've always pronounced Flareon the same way you do. 'Flare-aa-on' sounds really weird, and it doesn't make sense, since there is no long 'A' sound or whatever in the name, and 'eon' is NOT pronounced like that.
And you'd think the name would be pronounced the same as the other eevee evolutions. We don't say 'Vay-por-aa-on' or 'Jolt-aa-on', now do we?
Maybe they just made a mistake or didn't translate correctly or something?