I couldn't wait so I set it up
... the replication is working fine.
But, it seemed like the ISPConfig on the secondary server wasn't acting on the changes when they came over via replication (for example, add a new site, modify co-domains, etc etc etc). And I did verify that the items were replicated properly.
I will do more testing to verify (in fact I have a number of updates I will be making to the primary server to thoroughly test this out).
EDIT: BTW, I noticed that just one thing is not replicating in Drupal -- menu changes; if I change the menu structure/order/etc for a site, they don't seem to happen on the secondary server ... everything else is fine. Right now I can work around it by doing it manually, but I more than a little curious as to why since the entire Drupal database (except cache and search data) is being replicated)