I wouldn't say there's 0% risk involved in the setup you have, and I don't have personal experience with that setup either. But there are dozens of threads on this forum where people talk about the bans they've received and in all the ones I read, the general consensus is that Blizzard suspends/bans on a per account basis. Lots of people with 2 or more accounts on the same battle.net have said they got banned on one account but the other account(s) weren't affected at all.
I wouldn't rule out the possibility that Blizzard may put all accounts on the same battle.net under scrutiny if one of them is discovered to be botting, but at least from what I've seen if you don't bot at all on one account, it probably won't get disciplined, even if it shares a battle.net with an account that's been banned.