Unfortunately this doesn't apply for warranty repairs directly through Apple, as Apple won't bother using this port. They'll just tell you you're SoL and happily remind you of their iCloud services for backups. I had this happen to me on my 2016 TB MBP where the logic board had issues detecting the power level of the battery and wouldn't boot. I knew of the port, and asked them to use it, but their response was that the warranty would only cover like-for-like repairs and that I was responsible for backing up the data. Fair enough, except that Time Machine can and will lie to you about whether it actually backed up the data on your machine. Which is exactly what happened with my machine when I got it back and attempted a restore. Thankfully I had a separate non-Time Machine back up that I could use to bring my data back, but it wasn't fun manually restoring my OS profile and settings. I even managed to get a CS rep to confirm with me over the phone that I was not the only person to have had this happen to them.
Apologies for ranting here; I just hope I can save another person from this BS if they attempt to rely on this port. Through the entire process no Apple rep would confirm the existence of the tool so they made it seem like I was forced to use them for the warranty repair with total data loss.
If I may ask, samcat116, what's the normal procedure for handling warranty repairs at a certified repair center like the one you work at? Is it just labor cost, with parts billed to Apple? And does that include the copying of the data off the SSDs? I'm imagining for warranty repairs the easiest way to handle them is to just swap the logic boards out like Apple does and not bother doing actual diagnosing at the board level like https://www.youtube.com/user/rossmanngroup since the customer isn't paying for parts?