So it took me far longer than I'd like to admit, but I finally got ezMaster set back up. I spent what felt like forever trying to get their ovf file to work (extract that and the vmdk from the OVA they provided as I'm running proxmox), but eventually just gave up, created a new base VM, then imported the VMDK - sooo much easier, ugh.
I got a couple of the switches added, no problem (ECS1112FP, as well as an ECS1152) - kinda figures I guess, as both have full local mgmt GUIs. The ECW APs though, they don't have any check codes printed on them, so they're unable to register... I used to have an ECW230(v1) that I swear had it printed on it, but unfortunately I no longer have it to check (got soaked when water was coming into the basement from the room above and went to recycling

)
I'm going to reach out to engenius support when I get a moment to see if they've got some alternative method for those who wish to have local mgmt of the newer HW - I'll update here after.