Still new to this! Can you grow 2 rockwool cubes in 1 pot of clay pebbles? If so does it have to be the same strain .
This is a common practice in the flood and drain table grow scene. Most plants are started in rockwool cubes or other similar mediums to clone or for early veg and then transplanted into the flood and drain table of hydroton gravel for flower. It's not a problem. The one issue is rockwool cubes tend to grow algae on the top of them sometimes. You can cut a circle of foil and put a slit in it to the center along with a hole. Put it on the bottom of the stem and the light it blocks will prevent algae from growing on the top of your rockwool cube.
If you're talking smaller pot you could run into issues if the pot is too small or if the plants have way different maturing times, light tolerances, or growth rates. One plant might way overgrow the other. It's probably not best practice.
One thing people that argue against this idea might not understand is plant root systems have symbiotic relationships and will share nutrients. It could benefit the plants if they are similar enough.
If the pot is large and you train the plants apart from each other you can get away with two in the pot. I would be finishing in at least a 10 gallon with two plants.
Plants that share a roots system will help each other and compensate for each other's weaknesses. From Tree to Shining Tree