Putting it on dollies would be the safest way but you might not have enough room to jack it up if the garage is small. I believe if you take the tow strap and wrap it around the bumper where the bumper is bolted to the bumper brackets so that you are pulling on the bracket as well as the bumper, then you can drag it out with another vehicle.
I wouldn't recommend that method; depending on the severity of it being stuck, (and the direction of
the pull on the channel section of the bumper) you could quickly turn the bumper into a "V" with the wrap-around ends putting nice divots in each rear fender.
Now if vette meant to attach each end of the tow-strap directly to the bumper-mounting brackets, where they exit the body, that I could endorse. But again, depends on how great the car's resistance to move is...
As for the dollies__of whatever design intent__that all assumes he has a smooth concrete driveway; would be a disaster on grass, gravel and even my paver-driveway! I can envision the front tires pulled off the rear edge of (whatever type) dolly, and catching on the front shroud with a really expensive outcome.
If it was mine, I'd get a tow-strap, or decent rope, and attach to the rear crossmember between the spring shackles and the chassis__not a lot of room there, so the rope.strap can't shift. Rope, being somewhat elastic, would give the gentlest tug, and maybe the best choice. I mean, you're only pulling it a few/several feet right, not down the block?