Could a nuclear war result in massive flooding?

Yes, if the explosions result in a melting of the ice caps.

Not sure why anyone would be dropping nukes on the North or South poles, but its possible.

All we can do is model the possible effects of a nuclear war but current modeling technology is only good for very broad predictions; nothing as precise as what will happen after a nuclear war (or increased CO2 levels for that matter).

The typical prediction is Nuclear Winter which contemplates that an enormous amount of debris will be sent into the atmosphere which will, in turn, block the rays of the sun. It's a theory that is akin to how the dinosaurs became extinct.

Theoretically a thick cloud cover could create a greenhouse effect that would super-heat the surface of the planet without the benefit of direct sun light (see Venus), but it's unlikely that such an effect would follow shortly (relatively speaking) a nuclear war.

Virtually all predictions suggest that a freeze, not a warming will ensue after a nuclear war spews millions of tons of debris into the atmosphere, and a freeze will not cause massive flooding.

There are plenty of reasons to avoid a nuclear war, but I don't think massive flooding is one of them.

It could sure as hell ruin your day!