I have an accordion which is structured like:
<section... role="tablist">
<div>
<h3 role="tab">Title</h3>
<div role="tabpanel">
...
</div>
</div>
</section>
Does tab have to be a direct child of the tablist to conform to wai aria best practices or is it okay to be wrapped in a div?
Authors MUST ensure elements with role tab are contained in, or owned by, an element with the role tablist.
Your example is therefore correct.
I would suggest you read through the spec to ensure you are following best ARIA practice.
For example adding the role on a div as opposed to a section element, as per the best practice example.