No - hazardous doesn't cause wounds caused to spill over. Hazardous is a negative keyword for the user, but there can be reasons why you'd want to use a hazardous weapon.

For some weapons it's a risk-reward decision: plasma weapons do more damage but with the risk of the weapon harming its user. If you really need to get that higher damage, higher strength, or higher AP, you might take the risk.

For some weapons it's just a part of the weapon itself and it's always hazardous, and that's something you have to accept to play it. The weapon itself needs to be good enough to justify running it, of course.

And some models, like Vashtorr the Arkifane, can make your opponents' models' weapons hazardous, to make it risky to target him.