> Is there a bar between the bottom-bracket and the rear wheel on the non-drive-train side of the bike, or is it actually cantilevered in two dimensions?

There is no seatstay on the unseen side, but the Ventum is at least symmetrical. My boss' TT bike is similar in design to Cervelo in the second link, but with an oversized chainstay on the non-drive side for claimed aerodynamic effect. It looks fine with a disc in, however with a 5-spoke it looks dangerously pre-broken to my eyes.

I understand feeling uncomfortable with the design, single-sided front "forks" are my personal cut-off for that queasy feeling.

Plus, if you've not seen TT bikes in person before, be prepared for weird buffeting sounds from the disc wheels the first time you do. They definitely won't make you feel more comfortable about them ;)