We used to stand our Hunter Delta on its keel to scrub and antifoul. The keel is iron and held in place by four pretty massive bolts with their heads below the hull. And we were careful not to dry out where significant swell was likely.
No you would need to hang the boat in slings to get the whole dagger board exposed for scrubbing. Or strand the boat on the dry and lay it over sideways to allow the board to be extended. Not easy to lay it over.
I have had my little 21fter with dagger board type drop keel on swing mooring for 38 years.
I can access the top half of the dagger board from inside the cabin for painting with a/f. I have modified the trailer so that if the boat is pushed back about 20 cms the board can be dropped to the ground. If I jack up the trailer by about 15cms enough of the board is exposed for painting the bottom half.
As for scrubbing I do that in water using mask and snorkel. Fortunately water is not cold. Unfortuately water is not cold so weed grows quickly necessitating scrubbing weekly. A/f is effective alone for about 6 weeks at start of each season. My advice get a wet suit and mask and snorkel. ol'will