Yes later on I found all these details on some PDF's I found on this product and it describes in all detail these outputs. Yes they are open collector so I can apply my own pull up voltage and read when it get grounded.
About modbus, honestly if I have the chance to work down to the pulse level with all these devices and Im still using low-level microcontrollers (Arduino and its variants) and not a PLC I would prefer to use a pulse output
Thanks!