Not quite sure what the question is getting at. You mean if you want to wet yourself on purpose (as opposed to just going in the toilet), do you need a diaper to be able to do it?
If so, answer is no, but I'd much prefer a diaper. When I started out with this stuff I did occasionally experiment with wetting clothes. Later realised diapers are much easier to deal with as I didn't have to wash clothes and avoid wet beds and sofas! I could still wet clothes on purpose if I wanted to, but I don't want to.
Separate issue, but I find pooping far easier with a diaper. Using a toilet I poop at specific times and can go days without going. When I do I have to push it out hard and hate it. Wearing a diaper I'm far more relaxed and can feel the need to go at any time. I may hold it if the diaper isn't full, but sometimes it's hard as I just have an urge to go. Relax and it just comes out!