When the DH is in force, the AI seems to ignore the DH when substituting for a player injured out for a couple of days or resting.

Normally, I carry a catcher, first baseman, two infielders, and two outfielders on the bench. When the DH is in force, one of these reserves serves as the DH. If the catcher or the first baseman are the DH and the regular C or 1B are rested or briefly injured, the AI does not move them over as replacements, but sticks and infielder or outfielder into the slot.

In a recent dynasty, the DH was the reserve catcher. The regular catcher only caught 130 games (no long injury stopped play). The other reserves split the remaining 32 games at catcher while the actual reserve catcher logged 162 games at DH.

I would think that the AI would do a better job of substitution.