I've only heard it pronounced A-kay-see-ah and only then as the name of a street, not a person e.g
Acacia Avenue.
I think in the UK we tend to pronounce names like that with an extra syllable e.g.
Anastasia is An-a-stay-sha in the US and An-a-stay-see-a in the UK. Same with
Lucia - Lu-sha in the US and Lu-see-a here etc.
Sorry to go off topic. I have no opinion of
Acacia as a first name.