It does create a MITM vulnerability, the question is just whether it matters or not. With HTTPS a third party will only know which url you're accessing. With HTTP they can see exactly what data is transferred and can modify that data at will.

So adding HTTPS here accomplishes:

• hiding which exact page of the hacker's dictionary you're accessing
• hiding the exact contents of the page
• ensuring that this page doesn't get modified in transit

None of these are really an issue, so using http in this situation is fine. In general though, I'd consider not having HTTPS as a bug for most sites, unless you're extremely resource constrained on either side of the connection and you think carefully about the security and privacy implications