Pumpkins have hollow stems which are much loved by the squash vine borer.
If any of the borers escape into your soil, the effect will be to double the attack upon your zucchini and any other summer squash you wish to grow. Pumpkins require more space than any other vegetable you can grow, and the output of useable pumpkin flesh is less than anything else you could grow in the same space. Pumpkins are such heavy feeders and drinkers, that more soil amendments and more nutrients are required than for any other crop you can grow. Pumpkins attract squash bugs and cucumber beetles in greater numbers than other crops which are attractive to those insects. There are very few organic controls for the bugs that like pumpkins.