If it were up to me, Intimidate would function quite a lot differently, and be tied in to hate aggro instead of overriding it. Maybe something like this:
A successful Intimidate check would do two things: it would first give you hate as if you had inflicted damage, and secondly it would put a multiplier on that creature's hate for you equal to 120% + maybe 10% per point by which your result exceeded the DC. That multiplier decreases by 20% per second until back down to the basic 100%.
That means that if you've done 500 damage and a barb did 1000, then a successful Intimidate might raise you to 550 hate, and furthermore apply a multiplier of from 120% to 310% (or even more if your skill is ultra-high). Thus your effective hate would be from 660 to 1705, meaning you might not necessarily pull aggro from the barb, because his damage was so far beyond yours. The peak 1705 hate would gradually sink down to the "real" 550 hate number, although you'd probably have added some actual DPS hate during that time.
Obviously, that system would change Diplomacy in an equivalent way: a successful Dip check subtracts hate and then temporarily reduces your hate with a multiplier of 80% - 10% per point past DC. (Obvious problems could occur if the reduced hate wasn't limited to nonnegative results)
Note that without knowing the details of the hate system, the above-suggested numbers are probably wrong. They're just a demonstration of the sort of thing that could be done: taunt / de-taunt features that cooperate with hate, without overriding it.