We're working on the grading/evaluation features on the employer-side right now. This is something we're excited about, because it allows for more people to give input in the hiring process and opens up the possibility for coordination among companies as we're doing with the YCommonApp.
Always happy to hear what real people find useful :) Feel free to email me (nick [at] hirehive.com) if have you any other suggestions or questions if you try out the service.
2) It's a lot harder to "cheat" on a realtime exam, especially on video. The purpose of the interview is to evaluate a candidate, and it's unlikely that candidate's much smarter (or paid) friend would be part of the long-term package, but it's entirely possible someone could be getting assistance during the interview. (it's basically like when a law or consulting firm sends a partner to win the business, and then has summer associates doing the actual work once they're engaged...)
Assuming remote-interview-only, this would be a problem. Also, I view in-person interviews as fundamentally somewhat random. If you really like a candidate on paper (or on video), and he shows up and is close but not necessarily 100%, a lot of interviewers are willing to explain away problems as "he was nervous" or "having a bad day". Once an interviewer emotionally bonds with a candidate, it's a lot harder to be objective -- this is why I like to do early-stage objective/automatic screenings to determine basic competence.