Thanks - that document and others don't seem to mention vesting.
This leads me to believe that vesting isn't an issue - that as long as the strike price is the same as the share value when the option is granted, whether/when it vests (and what the price might be as it vests), isn't an issue. (Of course tax has to be paid if it is later exercised.)
However, this isn't clear; in particular, I've read that RSUs are taxed on vesting, so it'd be great to read something clarifying the situation with options, or hear from others who have seen this before.