Hi a victim, thanks for coming here with your question. It's a lot easier to discuss things here than in the servers.
Probably the best thing to do would be to send a PM to Yoda and ask him about it, get his take on things. If he was having a hard time keeping the server under control, then I could understand his asking you "leave the adminning to him".
To answer your question directly, in a messy server (or at least one where the admin is having to work hard to keep things on track), it would be better to just let the admin know rather than addressing the rule breaker yourself. The main concerns when guests ask other guests to follow rules are:
1) The guest being instructed on the rules may not care for a non-admin telling them what to do (even if they're right) and their response may not be gracious (ex. "shut up noob"). As you can imagine, this could start an argument and is something the admin would have to handle before they can investigate the original problem.
2) The guest asking people to follow rules may not be correct in their assessment. I'm not saying you were wrong, but there are a lot of newer people playing the Race gametype who call out "camped" when they were killed legitimately. If you've ever had someone accuse you of camping or anything else, hopefully you understand what I mean here. You may be able to brush off a false accusation, but others can't and it starts a conversation that could turn into an argument and now the admin has to stop and type at them, unable to check on any possible camping.
3) It does sometimes happen that guests in the server spend too much time trying to "control" or admin the servers. One quick "please don't chase" is fine, but some people will stop racing and investigate things and use all their time in the server doing this, rather than actually playing. The assistance is appreciated but we provide the servers so the guests can play and enjoy themselves. Also, the first two points come up here.
Even in a calm server, it might be better to let the admin know instead of talking to the other player, but it's up to you. I only say let us know instead because there's not much you can do yourself if someone's breaking rules and it's faster to type "erik chasing kills" than it is a request for him to stop. Plus it's not so personal and Erik is less likely to attack you for it.
Sorry for my long-winded reply! If you see something going on that can't be ignored or that keeps happening, I think it's great that you let us know and I thank you for it. If the admin says they'll take care of it, they do so in an effort to not create any new issues. It doesn't always come out as warm and fuzzy as it could, but there's not much you can do with 65-character limit and people shooting at your face.
Thanks again and good luck out there