Got some good ones here, so I'm gonna try to sort them all out
First, on the subject of action dice, from out of the errata, "Abilities that grant a bonus to action die results apply to each action die rolled, regardless of the number of action dice spent to prompt the roll."
For the most part, I'm fairly clear on this. Abilities like the Wheelman 'Driven' give you two dice to roll per action die spent in certain circumstances, and both die get the bonus. However, I'm not entirely clear on how an action die that explodes would interact with this. Does the explosion simply count as a continuation of the same die, or would it count as a second die?
An exploding die is still one die, so the bonus is added to the total produced by that one die.
Or, in real example terms: A character with a +2 insight to action die results rolls a d6 action die, getting 6 then 1. Are the results 11(6+2+1+2) or 9(6+1+2)?
Die roll = 7. Bonus = +2. Result = 9
Second, Ambush Mastery feat: Ambush Mastery allows Sense Motive to function as a synergy skill for Tactics/Ambush checks, however both the Synergy skill chart at the beginning of the skill section, and the entry for Tactics in the skill section state that Sense Motive is a synergy skill for Tactics/Ambush checks by default?
Yup. It is a superfluous statement.
Following that up, with Ambush Supremacy. The feat mentions shortening the time taken for a 1-hour ambush check, and yet the skill description lists one minute and ten minute ambush checks(I assume the ten minute in the skill description should be hour or the hour in the feat should be ten minute...)
The feat is in error. Its shortens a 10 minute ambush.
Sneak Attack damage: I thought I'd understood this, but now I'm not so certain anymore. It seems like sneak attack damage tends to be granted in one of two ways. Either abilities/skill checks grant a direct "You do so many die of sneak attack damage." (For example, succesful ambush checks "...each attack made by you or any helper during the surprise round gains 1d6 sneak attack damage."), or they grant "the ability to inflict 1 die of sneak attack damage." (For example, Scout and Assassin class abilities and Ambush Basics).
Same thing, and it s stacks. Some sources of sneak attack damage are conditional - like Wolf Pack Basics/Supremacy that require that your target be flanked, but overall it all just stacks up.
If I'm reading this correctly, abilties/checks that simply cause you to do sneak attack damage(Tactics/Ambush checks, the Knife Basics trick, Knife Supremacy benefit) should function even if the target isn't Flanked/Vulnerable/Helpless, whereas the 'general sneak attack dice'(such as Scout and Assassin classes and Ambush Basics grant) require the target to be Flanked/Vulnerable/Helpless?
Critical element is the definition of sneak attack damage itself (page 339). If you don't meet those conditions, it oesn't matter that you're doing Xd6 sneak attack with every single attack - you only get the extra hurt on the guy if he flanked, helpless or vulnerable.
For a real world example, take a level 4 Scout(may do 1d6 sneak attack damage). Sets up an ambush, crits the roll(two half action surprise round, every attack during the surprise round does 1d6 sneak attack damage). The target starts Flatfooted due to being caught by surprise by the ambush, and is thus Vulnerable. First attack at the target hits, does 2d6 sneak attack damage(the scout die plus the ambush check die). At this point, if the target survives, they are no longer Flatfooted since they took damage and are thus no longer Vulnerable. The scout takes the second attack and hits, it would only deal 1d6 sneak attack damage(the 1d6 from the ambush check still works, but since the target is no longer Vulnerable the Scout level based sneak attack die no longer applies).
It ends up that none of it applies because the target is not flanked, helpless or vulnerable. If the scout had a partner to flank the person, he'd still do his extra 1d6.
Hope that helps. I'll get the 1 hour/10 minute thing in the feat flagged for errata and we'll eyeball Ambush Mastery to see if any changes are called for (other than deleting the extra line).