Still crushing the rock is an activity you'd not do without the goal to bind co2. If the CO2 equivalent of the energy required for this is higher than the amount of CO2 that can be offset by the rock dust, it becomes a CO2 producing activity in total.
If your energy generation process is CO2 friendly you might simply offset other energy use with this energy and generate a better CO2 balance by this, skipping all the rock crushing.
The other question is, what if you do not have the rocks on site?
Transportation of tons of material is not free either. Neither is spreading it on field (labor notwithstanding).
That said, if farmers are already putting tons of imported materials, this could be a matter of switching it up. But if it would be better just to not do this, the whole thing just starts to look silly and worth it only locally at best.
If your energy generation process is CO2 friendly you might simply offset other energy use with this energy and generate a better CO2 balance by this, skipping all the rock crushing.