I've seen this done in some settings as well; the 'wipe and install the system' VLAN and the 'normal behaviour' VLAN. When you want to reinstall a server you tell it to reboot and then swap the VLAN; once the installation is done you swap it back.

Alternately, you can have your DHCP server be aware of all of your systems and know which ones need to be reinstalled; then just configure every server to network boot by default with a short timeout. If the DHCP server thinks your system needs to be erased then it serves a boot/wipe/reinstall image; otherwise, it doesn't and the system continues to boot normally.

Now that I think about it, I think our admin system for the DHCP server was how we handled it instead of VLANs. Also helped with automated installation of Windows on desktops, bootstrapping servers, etc.