I suppose in principle that the DNS entry leaks a tiny amount of information, but assuming your DNS servers are tied down against third-party zone transfers, the only way to extract this from the DNS is to know it exists, so no information leakage there. Most ssh attacks come from bots stepping through the whole IPv4 space looking for responses on port 22, and DNS entries have nothing to do with that.
I would probably name it something innocuous, though:
ssh-gateway-to-the-vital-code-repository.example.com is not a great idea.
As you note in passing, there are a bunch of other measures well-designed for securing a jump box (including non-standard sshd ports, rate-limiting, disallowing password-based authentication / requiring 2FA, hardened OS). I'd put a lot more time into them than into worrying about my DNS entry.