I deal with the process instruments which the other stuff on this particular forum, not analyzers, but I'm also a Modbus guy, so this topic of Modbus on an Ultramat got my notice.

The Ultramat documentation mentions an RS-485 port, but does not mention Modbus.  There is no Modbus address/register table in the documentation. 

Conclusion - the Modbus protocol is NOT available on the Ultramat.

A quick web search reveals a VERY long thread on the National Instruments (NI) site on the use of the ELAN protocol (over the RS-485 port) on Siemens Analyzers.  The thread mixes another brand analyzer and I haven't read the thread so I can't comment on how well it approaches the Siemens protocol, but you can take a look. 

https://forums.ni.com/t5/LabVIEW/I-am-looking-for-some-information-on-ELAN-protocol-for-Siemens/td-p/146247?profile.language=en

There is or was a ProfibusPA/DP option for the Ultramats, because I got a Google hit on a Profibus manual.  There are Modbus/Profibus protocol converters, which might be an approach to getting data via Modbus.

If you're not familiar with both Modbus and Profibus protocols then finding a system integrator to do the work might make sense.

The ELAN protocol that uses the RS-485 port is briefly described on pages 59-62 of the current Ultramat manual, along with software and related firmware updates.

https://cache.industry.siemens.com/dl/files/616/84233616/att_827672/v1/ULTRAMAT_23_english_en-US.pdf