It's not a direct link because it's a dynamic page popup thingy, but go to this link. Click on the Technology link, and then click on the "Road Tubeless By Design" pane. It contains the following verbiage:

"Drawing on our experience designing and making the world’s best mountain bike rims, the SES 4.5 AR Disc features a hookless bead profile and tire-bed bead seat lock. This design prevents air loss from impacts or aggressive cornering loads, allows for an exacting tire and rim interface, improves air flow from tire to rim and saves weight. Non-tubeless clincher tires are not recommended but tubeless tires can still be used with tubes."

Then further down it says: "Can be used with inner tubes, in tubeless tires only"

To be fair, it's not just he who is assuming that. In this article Jan Heine discusses some differences between tubeless and tires running with tubes in terms of their ability to hold onto a bead hook, the consequences of bead stretching, etc. While it doesn't directly relate to a non-hooked mount, it takes little imagination to understand that if a typical non-tubeless tire's bead is looser and potentially stretchier there may be issues with how well it will stay put in a non-hooked well. I'm still looking for the definitive article that directly discusses the difficulties of using non-tubeless tires in such a non-hooked tire well, but the concepts I have seen so far make ENVE's recommendation against using non-tubeless ready tires in their non-hooked tire well seem credible, and worth abiding by.