No, it won't happen. A zuke is a Cucurbita Pepo, the Kabocha is a Cucurbita Maxima. Pepo and Maxmima cannot cross. Neither will cross with Cucurbita Moschata, the butternuts.

Just be mindful that if someone else growing squash, nearby, they can still get crossed. Technically one needs a mile of isolation to grow pure seed this way. I'd feel pretty safe at 1/2 mile.

Hand pollination is a good way to ensure pure seed.

George
Tahlequah, OK

Here is a link that might be useful: Hand Pollination of Squas

George, How are those so il white squash doing for you? I just got around to planting all my pumpkins and squashes last week. Too much rain, and now the heat is on--upper 90's all week. Everything is germinating really fast tho'. I'm glad I ran into your pollination pics again. I'm trying it this year as I did not isolate anything. Oh, I hope to get your beans in the ground in the next day or two. I've got the first rounds of bush beans planted but haven't had time to get to the pole beans yet.

Brook