I haven’t checked the rights they want since I have no interest in DLive but I’m assuming that they have full account access.
Given that they can post through your account (to DLive), they can also comment. That’s a rather logical use of the posting key otherwise you couldn’t comment on DLive when logged in.
Could they ghost comment? Yes, if they wanted to do so.
this should be fixed, banned or a massive red flashing warning saying, 'we can fuck over your life if we want'.