It might work Ivan if you change the jaws. Remember, they grip on only 2 corners, btw -- they are 2 jaw, not 4 jaw. The bit grip length is much longer on a brace bit than it is on a tap.
re. alternative 4 jaw holders:
Another possibility might be to remove the cross bar from a tap wrench, drill a hole in some bar stock to fit the wrench body and attach that to the quill -- maybe with a Morse taper.
The wrench could either be permanently part of the MT blank, by brazing say, or removable with a flat and set screw. The hole would have to be close bored.
Maybe you could also turn the bodies of different tap wrenches to a common size to fit the MT blank. Then you'd need only one taper blank.
This would allow you to change out different size tap wrenches.