Are you sure that's true? I haven't seen a Hermit sample firsthand, but from everything I've read about it targets did not need to install an MDM profile, they simply needed to click a link. Looking at Apple's distribution guidelines - https://support.apple.com/en-bw/guide/deployment/depce7cefc4... - MDM is listed as one option, and simply going to a link is listed as another:
> There are two ways you can distribute proprietary in-house apps: > > Using MDM > > Using a website
It seems like the latter was used, so I don't think installation of a custom profile was required, which brings me back to my original question of whether Lockdown would have prevented it.