My thoughts are these:
- Whatever Crell Moset did, has already been done. No amount of moral grandstanding can undo it. The knowledge he gained IS OUT THERE. It can't be undone.
- Therefore, I can see no reason why the results of his actions should not be used. Letting B'Elanna die would not bring back any of those who died because of Moset.
- And it would not 'condone' his research practices - not only was the real Moset nowhere near the ship (so it's not like he would find out and thus be inspired to do it all over again), but also: None of Moset's data and research practices were actually used on B'Elanna! She didn't benefit from anything Moset did during the occupation. Moset was used as a fellow doctor in this episode, but nothing he did to any innocent victims was used in helping B'Elanna.
- Indeed, it might be a worse crime to NOT use the data - because then all those people died for nothing.
- So the hologram looked like Moset. Not a big deal. The hologram was not the REAL Moset. The hologram could have been made to look like anyone or anything. (Thus when the program was deleted, obviously it's not a big deal, because the Moset hologram was not a sentient lifeform like the EMH is)