So if you are ever in a pinch and need to use a piece of optical media, you can operate the CD-rom door via Command Line when you SSH into your ESXi Mac Pro.
(Enable ssh in the Security Profile of the Configuration tab on the vSphere client. Remember to turn this off after you are done.)
$ ssh firstname.lastname@example.org
# cd /dev/cdroom
# eject vmp.*.*
That will then eject your tray, leaving you to wondrously explore legacy optical media that no one wants.