The analog output 6ES7 135-6TD00-0CA1 manual states that the card is a HART master (Page 15).

https://cache.industry.siemens.com/dl/files/400/109768400/att_1262231/v1/AQ_4xI_HART_manual_en_US_en-US.pdf
 

Having the AO card be a HART master makes sense for the bulk of the applications where it is an analog 4-20mA output connection to a valve positioner, which is HART slave.   As a HART master the AO card can poll the positioner for diagnostics or send commands to it.

But I suspect that a flow meter HART master will not talk to an analog output card HART master.  A HART master talks to a HART slave, not to another HART master.