Lotus Elan and Lotus Elan Plus 2 Forums

Yes, I think that J technically only refers to the curve at the rim itself for getting a seal .
Having said that if there's a good seal it bodes well for tyre staying reasonably stable as a tubeless tyre won't deflate rapidly when punctured unlike a tubed tyre letting air out of valve hole.
The raised rib should help retain a deflated tyre until it destroys itself.
In the link you posted the key element is the H category for the 'hump' that controls tyre movement back to the centre well.

Also remember that tubes should only be installed inside tires requiring tubes. Tubeless tires ofter have internally moulded features that will abrade a tube and lead to a puncture.