Speed and Hit are the primary factors, though facing has a minor effect on accuracy (I've never noticed exactly what %), and some Evilities affect accuracy (such as the Ninja having 50% base dodge change if attacked from the front and Mothman having a 50% dodge change for projectiles or something). Weapon types have no affect on accuracy beyond the basic HIT bonus/detriment they may or may not have.
As for a specific formula I'm afraid I don't know. I just know that generally your HIT should be within the ballpark of the target's SPD or you'll either be sure to hit or sure to miss. Stealing has a much higher HIT requirement than simply landing a skill, too.
Also, the games will generally display "99%" when they mean "100%" accuracy. I'm fairly confident 100% accuracy is actually possible, as I've played enough Disgaea I really should have seen 99% miss, and I haven't.
Best I can tell the hit/dodge stuff has been mostly the same per-game, though later games have more Evilities that can affect dodge rate (and before Disgaea 3 the games weren't always transparent about what special attributes, now called Evilities, classes had).