I received a message from Adam yesterday before it went down about a withdrawal and it seemed like everything was fine. Obviously their server is having problems.
A 500 error happens when something like SSL or Apache gets misconfigured. It wouldn't be surprising if the DNS problems triggered an error and a service just needs to be rebooted. These guys seem to respond from noon to 6PM EST mostly, so they may have just not known about the problem or are trying to get it fixed. From my tickets with Adam he is not the technical person and he was working with others to get the server fixed for Heartbleed. I'm guessing they were updating OpenSSL on the btc-arbs.com server and/or the DNS server and something went wrong.
This is all optimistic, but the fact that people have been able to withdraw funds when the site was up during the problems is promising. Also, I was able to visit the IP yesterday and they had already posted Wednesday's results.
In short, calm down. Arbitrage won't have all of your funds stored on a server so even if it was attacked I doubt anything is gone. That's why large withdrawals take 36 hours, they have to pull it out of arbitrage and manually send it.