From the Downloads section of the SHN web site for downloading the current image, “Please also note that this file version is NOT compatible with EZBridge units shipped before 12/1/07!! Contact us for EZBridge upgrade details.” If your EZBridge was shipped after 12/1/2007 it is suppose to be compatible with the latest EZSrve/EZBridge image available which is 1.59 as of this post. Has anyone with a unit shipped before 12/1/2007 contacted SHN as requested and got different information?
You can skip upgrades. The XML database was changed at 1.54 so if you are migrating from an image before that there is a utility provided in the Downloads section to merge the devices and scenes xml files together. Again from the Downloads section regarding the conversion tool, “Run in the command line under Windows to convert the devices and scenes file to the single file format used in version 1.54.”
The EZBridge device can still be purchased so you should be able to bring an EZBridge up to the current image (not ignoring the 12/1/2007 question!).
Like any upgrade that is skipping many intermediate versions of software (or firmware in this case) it is often best to just start over from scratch with the latest version. Depends on how many devices, timers, macros etc you have defined whether trying to migrate very old stuff is really worth the effort. Again, this is independent from the question of hardware compatibility based on ship date.