It's an interesting way to think about the Hunley. Like I said, we ought to be impressed that it actually, amazingly, fulfilled its mission.
Still, a vehicle which appears to have less than a 50% chance of the crew surviving a mission would have to have success qualified in some way. Don't think those johnny rebs were signing up for a banzai charge.
As for the I-400's, I think Whiteshore's evaluation is what I was getting at:
Not a horrible sub class per se - just not the best use of the IJN's scarce resources at that point in the war.
I'd argue that by the Hunley's third and final mission (the time it actually managed to sink that US sloop) the crew must have known they were signing up for a suicide mission. After all by that point the Hunley had killed two entire crews.