Pretty sure chariots can not ambush,
that would be too nasty! Minos from the front and chariots from the side/back could kill nearly anything.
Ungor raiders with music can be good, makes it much safer to attack and win against small stuff in the backfield.
And yes, they are quickly shot into panic and run of the board, but that means, that the shooting unit shoots at 30-40 points and not at your hitters, which is good. AND they have to turn around to do so (getting -1 to hit) and have to turn back next round getting another round of -1 to hit.
I see it this way: They are one of the cheapest units available, to deal with them the opponent has to use troops worth far more than the ungors. Either to shoot them, which is OK as explained above. Or he has to actually dedicate melee troops to kill them:
Real units worth 100 points. Fine try to get me!
Small units like hounds, detachments ect. Fine less diverters preventing my hitters from reaching the juicy stuff!
Or he ignores them. Also fine, they march block, take out war machines, threaten lone mages, take shots at soft stuff and (very important i think!) lay crossfire to prevent flee reactions by the opponent and to catch stuff the minos broke.
Sure, i haven't tried them yet, but i will field ambushing ungors for sure! I will also try 10-12 ranked with music. In ambush this could be nice and still cheap, problem is what to do with the unit that does not ambush...