Neither species are known for eating snakes. The boa will not eat a BP. Not saying it's Impossible, just extremely unlikely.
There are other risks, like mentioned above though. There's really no benefit to having them both out at once, but it likely wouldn't be a problem. They'd probably just ignore each other.
I mean, if you're sitting on one couch with one snake and someone else has the other one out on a seperate couch I don't foresee any problems. Just make sure both people handling the snakes have experience handling snakes and are comfortable intervening if something were to happen.
Do the benefits outweigh the risk? Probably not.
And like the others mentioned, you've got to be sure to follow a strict quarantine process. I highly recommend at least 90 days.