Sophos SD-RED 20 and 4g LTE Gateway

Hello -
I've been searching the community for something like this but have mostly found people talking about the 4g module for the SDRED or using a USB stick LTE connection.

If we buy a 4g LTE router or modem that has an ethernet port for device connectivity (let's say someone could plug their desktop computer directly into it), wouldn't the SD-RED treat that as a regular uplink since it's ethernet --> 4G LTE Gateway -- > Internet ? I'm assuming IP addressing / DHCP is configurable. We wouldn't have to worry about compatibility either since it just has to establish internet out. Correct assumption?

We don't want to buy into a 2 year contract with a 4g provider to find out this is not a viable plan. Any thoughts would be appreciated.

Thank you!