Strictly speaking, by the black and white of the rules, correct, you can’t AoO an invisible opponent… and hence the use of the words ‘some DMs’. But I’ve seen one DM allow it, and it was a mighty compelling argument that he had…
True Strike is a divination spell that gives you a ‘…temporary, intuitive insight into the immediate future during your next attack…’ Effectively, the spell allows you to strike at your target at the most fortuitous time… so, if an invisible opponent did something that could provoke; the True Strike would kick in and guided your blow…
Does this break game balance? No. It’s a one shot… and there is no guarantee that it will work…
Is it in the spirit of the game? You bet. It’s a clever utilisation of a resource…
Is it in strict accordance with the rules? No…
And before anyone starts going on about, “…It’s wrong, it’s not RAW…” I know, but this was one of those things that, in my opinion, was a value add to the hobby… and after all, are we not here to enrich the actual playing of the game?
Coincidently, Li Shenron has just posted a poll asking, “How far would you go against the RAW to promote creativity?”… My answer, this is how far I would go…