Are you sure its blocking the actual hosts, or just forged "from"? Ive had no problems with it since it went on, amazed at the amount its blocking.
You will not be able to whitelist using amavis, because mail blocked with rbls wont get that far - its blocked on the initial smtp conversation. My guess is you are getting "false false positives" (not really false positives) because of forged "from"s
Test it yourself by sending a message from your gmail, im pretty confident it will arrive. Spam sent from gmail will probably be blocked further down the process by sa.
If you are actually getting false positives, try just using sbl.spamhaus.org - it is a lot smaller, so you will get more spam, but false positives should drop to zero.
**EDIT**
try using this (as the zabbix user) to list all the HOSTS (as opposed to from addresses) you are blocking (this is for ubuntu 6.06 - you may have to change your log location):
grep spamhaus /var/log/mail.log | awk '{ print $10 }'
or use it with tail to give you a constantly updating list on your console
