Using a vendor-supplied kernel means that there are extremely likely to be other people using most of the same stack as you, many of them on the same hardware. If there are problems, it's likely that other people have noticed the issue, even if the bug hasn't been found, so it's much more likely to get fixed.
If you compile your own kernel (and/or copy of Apache, MySQL etc etc) you're running something unique to you. If you have problems, you're on your own.
If you're paying for Red Hat Enterprise, use the Red Hat Enterprise packages unless there's a good reason not to. If something goes wrong, you can call Red Hat support and have at least a steer in the right direction. Custom-compiling everything just for the sake of it, just to have new 'shiny' stuff is crazy.
