Yes. It isn’t an uncommon construct. It is actually more common to not have a hurdle at all for this investor veto right on a sale, although companies usually try not to give one individual investor this veto right – rather it is preferable to require a majority of the Seed, Series A and B voting together as a class for the veto. If you have to give one investor a veto however then setting a hurdle like this is a common approach.
As for the threshold, anywhere between 1.5x and 3x are typical. 2 and 3x the most.