Do blue giants have a habitable zone? Or would the planet(s) need to be too far away for life to exist?
Just because a planet is in the "Habitable zone" doesn't mean it is habitable. A planet is said to be in the habitable zone if it is possible for liquid water to exist on the surface. A planet may be in the habitable zone, and yet not be habitable if, for instance, it's atmospheric pressure is too low (like Mars) or too high (like Venus), both of which are in the habitable zone of the Sun.

A star may be unsuitable for life for other reasons: it may be prone to extreme flares, for example. A blue giant is a star that burns bright and dies young, only lasting a few million years. Planets around such a star would have only just formed (they may still have molten surfaces). Blue giants tend to be unstable, being variable over a range of timescales, and ejecting large amounts of matter into space.

So while there would be a region which is "habitable" in the sense that the surface temperature of a planet could be in the range 0-100, you wouldn't expect such a planet to actually be suitable for life.