I believe do actually do a bit of counterspying, but I don't think they get valour increases for it. I remember a few times having no border fort in a province, but having a v2 or 3 emissary (forget which) and assassins and spies were being caught in that province.

As far as bribing goes, I could be wrong, but I don't think they get a bonus for bribing because the value of the army doesn't depend upon the skill of the emissary, but rather the vices and virtues of the general, and the units in the army.

Not only does a rear attack by range do more damage, but firing on units from an angle/flank/rear kills more as well. Even if you can't get a flank, firing at a unit from a 45 degree angle can help get past their shields for maybe a few more kills in a volley, not always though.

And I think you were asking about a rear attack if its uphill, like if you're being attacked uphill, and you bring units around the rear that attack uphill....I try not to do this unless the unit is by itself (not jumbled up with a few other units). Otherwise they sometimes take too long to route, and your rear-attacking unit takes more casualties than it needs to, fighting uphill. Instead, a flank attack may work better? At least then you're attacking downhill/on level ground. All depends on the situation though.