It's possibly to do quite a lot of blending with a bolt on neck. You can't do that same amount that's possible with a set neck, but it's an option. Even if you tried to glue it in (which is completely pointless in my opinion), there's no substantial heel, and thus, nothing to blend. I really can't think of a good reason to glue a bolt on neck in. The whole purpose behind bolt-ons is that if the neck goes south you can replace it. You're going to need a really tight fitting neck pocket to get a good glue joint, too.