Hi,
I have never worked with these devices myself, but looking at the Modbus protocol on wikipedia shows that some Modbus protocols communicate over UART, and Mathematica has a built-in Serial driver as of version 10.0+.
One thing that might complicate your application is that the Emerson devices you mention seem to only communicate with a specific transmitter, and Emerson doesn't seem to have much documentation on how one could interface such transmitters to external programs. If you know of any such documentation, that would be helpful to know
Ian
