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].
alternatively, donate to openbao the amount you'd pay for Vault support. you'll help ensure the project doesn't fall into disrepair and get more influence over fix/feature prioritization than you could with Vault.
While I'm sure Vault contracts run more than what I'd care to know, the project is set up under the Linux Foundation and I've been told in the past that we as a project are capable of receiving direct donations.
If you're so inclined, please do!
We'd of course be appreciative of it, but that said, the OpenBao TSC had tabled conversations about just what we'd spend any funds on until after we moved into the OpenSSF... Which just concluded which means it might be time to get things moving again. But just to say, we may not immediately know what we'd spend any donations on. :-)
(Alternatively, hiring and retaining a maintainer or a firm working on it would also be good options. Part of the growth requirements of OpenSSF projects is to have more than a handful of companies on project leadership so increasing diversity is a key goal.)