DougR
This can be done most easily and reliably by writing a daemon to audit the Apache/svnserve log files to notice failures and report them. If you want to do this solely with hooks then what you'll need is a daemon that receives communication from every a "start-commit" hook and then tries to match that up with a message from a "post-commit" hook. If, after a suitable amount of time there is no communication from the "post-commit" it can send an e-mail. This mechanism is unreliable since the post-commit hook is not guaranteed to fire/complete so could result in false-positive communication.