Has it ever been specified whether you needed sneak attack previously to use the bonus damage from unseen seer or not?
And if not, could you get around this by say...getting the hunters eye spell?
I have seen hunter’s eye as a common recommendation for unseen seers, to take advantage of this class feature, so it seems to me that the general consensus is, you need to have some form of sneak attack, sudden strike, or skirmish in order to gain the benefit of the extra damage dice, but the timing of gaining this unseen seer class feature versus gaining one of those features is not relevant. I have not, however, seen any attempt at a close reading of the text to justify this; it just always seemed accepted that this was the way the class feature worked. In my opinion, it is better this way than other possible alternatives. Even though unseen seer is a very-good class even without this feature, and it improves upon some of the best classes in the game (spellcasters), ultimately I think that these kinds of timing issues should be avoided as much as possible in the game, and as good as it is, unseen seer is hardly broken compared to options available for spellcasting prestige classes.
But a close reading of the rules text is still valuable. Therefore,
At 1st level, the extra damage you deal with your sneak attack, skirmish, or sudden strike ability increases by 1d6.
If we look at only the first sentence of the ability, as quoted, there is no appearance of a timing concern. When you deal extra damage with sneak attack, skirmish, or sudden strike, the damage is increased by 1d6. If you don’t have any of those features, you never deal extra damage with one, so whether or not that damage is theoretically “increased” is a moot point—you never trigger the damage in the first place. If you later gain one, then you can trigger it, and per this sentence, the extra damage you deal would be increased.
OK, so then, the second sentence:
If you have more than one of these abilities, only one ability gains this increase (choose each time you gain this benefit).
First of all, unless you have more than one of these abilities, you would be completely justified in straight-up ignoring this entire sentence since the initial condition is not met. Then you would see only the first sentence, which as noted indicates no concerns about the timing of gaining this ability versus any other.
This sentence does bring up timing, but there is an ambiguity here: when do you “gain this benefit”? Is it when you reach this level in unseen seer and gain the class feature? Or is it when you deal extra damage with one of the listed abilities that you gain the benefit? I would argue (with thanks to @annoyingimp for pointing it out) that the latter 1. makes more sense, 2. results in better gameplay, and 3. matches the general consensus that I have seen.
Reading “each time you gain this benefit” as “each time you deal extra damage with sneak attack, sudden strike, and skirmish” means that, for example, a hypothetical scout/wizard/unseen seer can choose skirmish when triggering skirmish, and choose sneak attack when triggering sneak attack from hunter’s eye, and just pick one when triggering both. That just seems reasonable to me—there is no double-dipping to apply the benefit multiple times, just picking one thing to apply it to each time you use it.
Even if you insist on reading things the opposite way, however, and that the clause indicates a single choice made for each time you gain a level of unseen seer with the ability, I would argue it could still apply to hunter’s eye. After all, this is an ability that all unseen seers have, regardless of whether or not they can use it. If an unseen seer gains one of these abilities after gaining this feature (e.g. through casting hunter’s eye), then that unseen seer still have the damage bonus ability—and thus, the damage they deal with the new ability is improved by this one.
An unseen seer with none of these abilities does not meet the If condition in the second sentence (0 is not more than one), nor does an unseen seer meet that condition when first gaining one of these abilities. But that clause is still an active part of the ability she has. On gaining a second one of these abilities, that condition is met, and then (for each iteration of this ability she has) the unseen seer picks which ability gains the bonus. Personally, I would rule that as the second of these abilities ever, even if the two aren’t happening at the same time (i.e. someone who cast hunter’s eye to gain sneak attack, and then later took a level in a class that gains sudden strike, would have to choose upon gaining sudden strike even if hunter’s eye was not active at the time).
The only way I could imagine justifying denying the damage bonus feature to unseen seers who did not have any of these abilities at the time they took this level would be if the text included a line like “If you do not have any of those abilities when you gain this ability, you gain no benefit from this ability,” or something. Since nothing of the sort is in the text, I would not be inclined to give much credence to claims that this kind of timing should be a concern.
Yes. To quote the pertinent passage:
Damage Bonus: At 1st level, the extra damage you deal with your sneak attack, skirmish, or sudden strike ability increases by 1d6. If you have more than one of these abilities, only one ability gains this increase (choose each time you gain this benefit).
Emphasis mine. It's pretty clear you need to have one of these abilities to increase. If you had none of these abilities, there'd be nothing to increase.
Sorry, didn't notice the edit immediately. I agree with KRyan's excellent answer. To summarize:
By RAW, Unseen Seer gets his extra damage on any of the 3 sources. Only if he has 2 or more need he lock in to one of them.
By RAI, The Unseen Seer gets his extra damage on any of the 3 sources, but only one at a time. (To avoid him having 1d6 sneak attack, 1d6 sudden strike and 1d6 skirmish and getting +3d6 from one level in Unseen Seer)
Either way, yes, he can benefit from Hunter's Eye and similar spells.