Couple of things to consider for your business:
1) If Vault's license format prevents managed hosted solutions, you might want to switch to OpenBao.
2) Vault has enterprise solutions you have to pay for; OpenBao is making those free.
3) In general, if you plan to pay for support, use Vault. If you don't plan to pay for support, use either of them, because they require the same amount of maintenance and have the same features. Since OpenBao is a fork, you can just review the ChangeLogs when you upgrade to see how far it has diverged from upstream. Once it's diverged more than you're comfortable with, you can just switch back to Vault [before you adopt diverged features] and it will be a very small change. You can also avoid using any OpenBao features which aren't compatible upstream.
It's worth considering that your business can lend legitimacy to OpenBao, which will increase its contributor share. You can simultaneously make a small, low-risk engineering decision, while helping grow an open source project [which helps your business].