Should I be able to run two different “close” code versions of wordpress with the same DB

A concrete example – I am upgrading to 4.1 from 4.0, the upgrade was successful but I discovered that a plugin broke. Can I just revert the code.

The real live issue I am facing is having two wordpress “application” servers behind a load balancer connected to one DB. When there is the time to upgrade can I run the upgrade on one of them (which will upgrade the DB as well) and realistically expect the other to keep functioning?

There are usually minimal db changes from one version to the next, it should be safe to do the manual-reinstall procedure with 1 older version.

You can see the changes it does in wp-admin/includes/upgrade.php