By the Modbus standard, no, because packet collisions result in poor or no communications.

With a separate bus arbitrator module between the Masters and the slave bus, Yes.

See these earlier discussions on the same topic:

Three bus arbitrator devices that have been mentioned:

MULTII-PORT™ Model 366-10P-XYZ

ICP tSH-73x serial port sharer arbitrator

ADF HC67146 bus arbitrator bus arbitrator