Hophornbeam is dense, hard and tough stuff - it works excellently when heat treated. The back is likely to be rippled so you just want to remove the bark for the back because you just aren't chasing a ring with it...
eg. be very careful when removing the bark/cambium
Hickory is not quite as dense in general and will need to be a shade wider. It is especially good in tension but not so great in compression so it's a very good idea to trap the back of a hickory bow eg. make the back narrower than the belly. The idea being that you are playing to the woods strengths. It's highly unlikely to break on you. Also good when heat treated.
When making bows remember that you need to understand the particular woods properties before just making it to set dimensions. Most woods when designed properly will shoot the same speed. Some woods make it easier to get a good bow because they don't need 'special' treatment but that doesn't mean x is better than y is better than z etc...
