Does the Exchange Service Pack Installer honor the /disasterrecovery switch?
Yes. When you run Setup with the /disasterrecovery switch, it installs the Exchange Server binaries on the server without touching any associated Active Directory (AD) objects. (See "The /disasterrecovery Switch," November 2001, InstantDoc ID 22380, for a more detailed explanation.) Of course, to perform a complete installation on a failed server, you must install both the release to manufacturing (RTM) version of Exchange and whichever service packs and hotfixes were running on the server before it failed. Therefore, the Exchange Service Pack Installer also supports the /disasterrecovery switch.
Be aware that when you use the switch with the Service Pack Installer, it doesn't remount the Exchange databases after the installation process. And for some reason, using /disasterrecovery with the Exchange Server 2003 SP1 Installer causes the Installer to skip some prerequisite checks—in particular the check for the presence of the Microsoft IIS compression fix described in the Microsoft article "FIX: IIS 6.0 compression corruption causes access violations" (http://support.microsoft.com/?kbid=831464). You'll need to manually install that hotfix before you install SP1.