I'm not totally sure how wide the gap is, but it is true that you can almost get your hand through it. I've never had the sensation that I might fall in, but I have a pretty big hiney, so I can't imagine that would ever be a problem!!

But to answer your question, yes, my sit bones stay where they're supposed to. I don't usually engage the nose too much when I climb... I sit way back on the saddle and spin up any hill that's spinnable. I mash when necessary, but never really notice the nose in this saddle, or any of the others I've had, for that matter, so I don't know if I can help there.
The saddle has a pretty padded back, but it doesn't feel squishy. My sit bones were sore after I rode on Sunday, but not until later in the evening. But I also don't feel like I need a ton of chamois to be comfortable. I rode 30 miles on Sunday with my most minimal chamois and was comfortable the entire ride.
I saw that bikemania.biz has the saddle (Selle SMP TRK) for $75.00 online if anyone wants to bite the bullet and give it a try. That model does come in both men and women's specific styles.