aggro is server/player side. server pops a mob that can aggro player then does something to aggro that mob.
As for enimity all that really does it make the time between provokes/flash/stuns increased. Your hate is dependent on CHR (this is my belief otherwise PLD af feet wouldnt have CHR+) hate build (I.E. damage done provoke/flash/stun) and enimity. Enimity and CHR probably have the least influence on hate holding because enimity in my opinion doesn't make a huge difference in holding hate seeing as though DDs can essentially pull hate whenever they feel like it. So in order it goes JA(spells)> Enimity> CHR. Enimity can give some hate because it rises over other peoples hate they have (see Sentinel when first learned and even now). Rampart gives alot of hate even when solo but I like to stack it with warcry because both boost my enimity levels because I am giving two buffs to the whole party with in a certain area. CHR just comes into how hate is held because if you think about it you have BRD XXX uses a song and because their CHR is so high they can take hate ontop of the fact that they're AoE buffs. That is just my take though and I think it can be generally agreed up to a certain extent.
Edit: So no enimity has nothing to do with aggroing something.
+Enmity makes you get more hate for each action, and makes your hate decay (both over time, and from stuff like getting hit) more slowly.
-Enmity makes you get less hate for each action, and makes your hate decay more quickly.
CHR does diddly squat for hate, and this has been debated to death. Its only effects are bard debuff resists, charm resists, intimidation rate, and a few secondary mods on things like Bludgeon and a dagger WS or two. (All things considered, it's arguably the most useless stat overall.)
AF stats are also not overly indicative of anything - if you look at AF for all jobs you'll see a lot of pretty useless +stats on them.
If you're talking about BRD buffs, Mazurka (pre-update) was the only one with significant hate and that was a trait of the buff itself. Otherwise, on normal mobs the only time a bard pulls hate by buffing is when they hit the puller with a buff *right* as pull comes in (generally before the initial voke/flash/whatever). Which is a factor of doing a hate-generating action to someone else with low hate (namely the puller).
As for HNMs, it's more a matter of hitting six people with buffs twice every two minutes or so, not getting hit, possibly spamming debuffs like elegy, and (the clincher) the fact that for some daft reason, a ridiculous lot of HNM-killing bards do not wear much if any -enmity, and instead go spouting their shiny Zenith or something. (Furthermore this only pops up on drawn-out fights such as wyrms.)
And yes, there've been tests showing that either CHR doesn't affect enmity at all, or if CHR *does* affect enmity in any way, it's such a ridiculously slight effect that it wouldn't be worth wearing CHR gear over anything else anyway. If you want more info on the subject, go browse around on PLD forums.