Interesting. I have multiple devices that have had successful simultaneous (shared) connections on port 2101 to the Elk from the ISY994, HS3, HS4, and the Automation Bridge. It is true that running Elk RP will block those connections. It connects securely on port 2610 and apparently requires dedicated access. So, I disconnected all of the devices that have had access through port 2101 to the Elk M1G. The Elk NS then connected and correctly created the nodes for my system. I then reconnected the ISY994, HS3, and HS4 successfully and all the devices and the Elk NS are able to share port 2101 successfully. M1 Firmware 5.3.10 MXEP firmware 2.0.44. non-secure access is enabled.
It would be a serious limitation if the Elk M1G couldn't connect to multiple devices since that would prohibit the utilizing it for home automation if you had it connected to an external service for monitoring.
keepersg's post in Elk node server can't connect was marked as the answer