Alloy wheels

[MarkDa]

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.

[CBUEB1771]

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.