The fix for this in Linux is to add the user to the dialout group. Unlike on Linux RT where the user is lvuser, the LabVIEW development instance is run under the logged in user, so add your dev account to the dialout group.
The next issue is that despite the documentation stating otherwise - the default mode of the cards does not appear to be 4-wire. Checking through NIvisaic through the Linux Terminal, the ports are default RS232_DTE. With the Wire Mode property being unsupported in Linux, it looks like I am out of luck correcting this. NI is looking into this, so maybe there will be a solution.
My system is LabVIEW 2018, Linux 2018 Drivers, CentOS 7.6.
I do have a LabVIEW 2019, with the LabVIEW 2019 drivers that were just released and CentOS 8 set-up coming to test out. I will definitely follow up if that fixes or doesn't fix the issue.
I tried a simple Loopback test, and it did not work. I then tried the same loopback test on the Rs422/485 DB9 loopback dongle on a USB-RS485 with my PC, and that worked, so the wiring on the dongle is correct for loopback (per NI wiring in their Serial Reference Guide).
As a follw-up: the Serial cards are now working, we did have to make sure the driver was properly installed originally, as noted above. Then we found an issue with the online instructions for the serial loop back test and the recommended cable to connect the RJ50 to a DB9 breakout for loop back wiring. The incorrect cable was called out on the instructions. The 192190-01 is not the correct cable. The 182845-01 is the correct cable that matches the usual serial pin outs.
You can use a 192190-01 but you need the pin outs to determine the correct pins.
I have attached the pin outs for the 192190-01 (192190A-01) and the 182845-01 (182845C-01) that were provided to me. I could not for the life of me find the pin outs on ni.com when I searched for any documentation on the 192190A-01. If I had a DMM with continuity capability I could have found the pin outs - but based on the NI documentation I was wiring them up correctly...