I just cut open a spaghetti squash and the seeds have started to sprout - it's still okay to eat right?

I have seen this, and the squash was fine.

I'm going to say yes. If the squash is not mushy or soft, has no off odors, and otherwise appears normal, I think it should be fine to eat. Squash seeds sprout very readily, so perhaps this particular squash just got ahead of itself!