Well Shorty- my short answer is that the tip hardness is neither a benefit nor detriment to making a bank shot.
My long answer is this: let's look at what affects bank shots ( we will look at one rail banks):
1.The point where the object ball strikes the first cushion determining the angle out to the desired pocket - not affected by tip hardness
2. Any english ( sidespin) that the cue ball imparts to the object ball - outside or inside spin, opening up or shortening the angle to the desired pocket- not affected by tip hardness.
3.Table cushion conditions- rail height, cushion density, humidity conditions, etc. all may affect angle out to the desired pocket and will vary from room to room, table to table, etc- but not be affected by tip hardness.
4. Speed off the first rail will either lengthen (slower speed) or possibly shorten ( high speeds) the angle to the desired pocket. I doubt that tip hardness will affect speed to any degree on a one rail bank so as to cause a missed shot.
So, in conclusion, using a tip hardness that one is satisfied with as a regular playing cue tip would be the best tip hardness to use whether the game is bank pool or some other game- IMO. You will deliver your stroke as you normally do in any other game, and make adjustments for all of the above four factors according to table conditions and the particular bank shot set up - without regard to cue tip hardness.