YESSS…of course they should. I can’t imagine using WYSIWYG in the first place, unless you’re just curious and checking it out. I feel like that’s for the person who doesn’t want to pay a designer. Ultimately, as a designer you’re responsible for the integrity of the site and part of that involves code that might need to be fixed by someone. At the very least, designers should be able to troubleshoot and fix something when an update breaks it, etc. Without developer skills you are dependent on a third party.