It may not be quite that simple. I haven't done it, so if Garry has then perhaps his input is more valuable than mine, but...
Different transmitters use different excitation voltages. Let's assume that both transmitters are set to a load cell rating of 2mV/V. So if your full scale is 50kg, then at 50kg, both transmitters will expect the mV signal to be 2mV multiplied by the excitation voltage. If transmitter #1 uses 10V excitation, and transmitter #2 uses 5V excitation, then with a 50kg test weight, #1 will expect to see 20mV (2[mv] * 10[V]), whereas #2 will expect to see 10mV (2[mV] * 5[V]).
If both transmitters use the same excitation voltage, then that problem is eliminated. But there's more.
With 6 wire load cells, in addition to the signal and excitation, you have sense wires. The idea of these is that they are joined to the excitation wires at the closest possible point to the load calles (in the actual load cell for 6 wire devices, or at the summing box or connection box for 4 wire load cells). The reason for this is that while your transmitter may be designed to put out 10V of excitation voltage, it may not be exactly 10V. It may be, say, 9.7V, which isn't a lot you might say - but all of a sudden it's a 3% error in your measurement. Plus, if there are long cable runs involved, you also have voltage drop to contend with. By the time your excitation reaches the load cells, it could have dropped to 9.5V. The sense wiring in effect tells the controller "this is what the excitation voltage is AT THE LOAD CELLS". So now your transmitter realises that the excitation voltage is not 10V, it's 9.5V. So it knows that 50kg is not 2*10=20mV, it's 2*9.5=19mV. And adjusts accordingly.
So. If you joined the sense wires to both transmitters, and just used the excitation from one transmitter to actually provide the excitation voltage, would it work? Maybe. You'd definitely have to be powering the two transmitters from the same power supply, but even so, I don't know how happy a transmitter would be about getting a "sense" voltage from a different transmitter. You'd have to try it out and see.
And finally, you have temperature compensation to consider. You'd have to, at the least, make sure the two transmitters were right next to each other and at the same temperature, but even then I don't know enough about how this works to be sure how they would react.
I guess the long and short of it is, have a play with it and see what results you get - but be careful of what happens to your accuracy!