Most Cadillacs have had Caddy specific frames and sometimes engines, though they have borrowed engines significantly. They developed their own engine not too long ago and barely used it, a DOHC V8 called "Blackwing", which led to confusion about the current CT5 V Blackwing, which doesn't use that engine. The Ct5 and CT4 use the alpha frame architecture, which Camaro adopted a few years back.
But the most obvious borrowing has been with the Escalade, which is of course just a Tahoe/Suburban with fancier stuff but same frame/drivetrain/etc.
It's by far their most profitable item. Their smaller "SUVs" are not very competitive vs competition.
I'm still quasi-interested in the BMW X1 but hope to hold off a few years thinking some better options will be available.