I kind of figured out an estimate on my own. Maybe it'll help someone else.
Ground clearance is 16", but it can lower 4" with the adjustable air suspension. So the bottom of the vehicle is 12" when fully lowered.
I'm estimating around 3 feet from ground to seat after looking at the various photos available online. The seat height seems to be almost even with the top of the 35" wheels (including tires) when lowered. The distance from the bottom of the frame to the top of the seat looks close to 2 feet, maybe less.
This is probably the best picture I could find to estimate the seat height. Not sure how much the prototype will differ from the production vehicle though.
Unfortunately for me, I think it might be just a tad too high for me to get into with my wheelchair being only about 2 feet high. Sliding up 1 foot is a tall order. It's a shame because the CT has a paintless finish, which would be perfect for me because I beat the hell out of the door area getting my wheelchair in and out. I hate scratching paint, but scratching stainless steel wouldn't bother me at all. Plus the truck bed has plenty of room for someone to stow away my wheelchair, which checks another box.
I've got a Model Y held on order (that seat is pretty even with my chair), but I'd really love to see the CT in person before I rule it out.