@nero243 in my experience e5 xeons can boot any ram that is supported by the board.
Had my 1650v3 running gskill trident z a while back, though that wasn't an ES, but i don't think Udimms are the problem.
It is nice to hear that you at least have one that posts, the most recent V3-ES i got to play with was shorted out, Postcode 00 and no Voltage from the VRMs.
To your postcodes, i currently assume that 5X so early in the Post process, before "bX" is something around "no ram detected" and bX should be Ram (init | training). 5X after the bX codes is something i have no clue about.
The last time i tried to boot a V4 Es on an Asus X99 board, it went through into the bios on the first try but after applying defaults, it was stuck somewhere. Probably Microcode related.
Maybe you want to take a look at the Asus Serverboards, Z10Pa /Pe, those, i think, have ES support. You might be able to grab the right modules from there bios.
Depending on where you are located, i could test it for you, or we could exchange or lend hardware. In my Case, EU, Germany.
@joe paolicelli you are right, if they have the crappy paste, it's most likely a dummy i9.
Though since deliding soldered cpus is a bit different then the i9s, i'm pretty sure you'd kill your sample in case that it is a soldered xeon W.
I prefer the Supermico c422.
I will check my two blanks for the shade and markings when i get back home this evening.