I have limited experience with sposies but wanted to respond anyhow
diaper rash is when the bottom gets red and irritated looking, it looks like a classic rash in my opinion. I haven't heard of sposies sticking to bottom before, is it really really wet when it's sticking? I would try changing him more often, trying another brand of diapers and making sure his bottom is very dry before the diaper goes on. What about trying some disposable liners in the diaper? They are usually for cloth diaper users but there's no reason they wouldn't work in this situation too. Good luck and congrats on your little one!