I just checked one out, and you are absolutely correct. And we all know that those low-profile tires wrapped around 20" wheels stick just as good as a tire with 3 times the sidewall.
Hmmm, lets see. According to Dodge, the Hellcat runs an NHRA certified 11.2 second 1/4 mile with the production street tires- so that's as equipped, right off the showroom floor. Yeah, that's pretty slow for a 4,449 lb car. 10.8 with street legal drag radials, but the specs don't mention the diameter of the rims used for the drag radials (if they changed or not). However, since the rear disk brake rotors are 13.8" in diameter, I would guess that they need to be at least 18" rims, because nothing smaller in diameter will fit on the car.
It's almost like tire technology has improved since they came out with the BFG T/A.