I haven't found any good SNMP modules to do this. However, you can do this yourself:
Using cron, dump apachectl fullstatus to a file like /tmp/apache-status.txt. Do this once a minute or so. Or parse out the information you want, and dump it to this file.
Configure the snmp agent's exec feature to run a command like grep yourvaluehere /tmp/apache-status.txt
Query that value using SNMP, as needed. Since /tmp/apache-status.txt is updated every minute or so, it is pretty up to date. The query will return the value of #2. You can do this for multiple queries/values.