I usually successfully grow cucumbers and tomatoes side by side (in separate grow bags) in my greenhouse
This year I have a space in a grow bag which has 2 cucumber plants in it, would it be ok to put a tomato plant in next to them? Will the plants grow successfully in the same grow bag or will it cause problems?
If you do cucumbers are slightly 'greedier' than tomatoes so put some slow release pellets around the root ball to give it the little extra it needs. Some suggestion that tomato yields fall if grown with curcubits but in a garden setting its not so important.
According to one of the experts in the garden center where i work it will be fine and you can feed them both tomorite, but.... cucumber like more moisture in the air than tomatoes, and tomatoes like less moisture so you would need to way to give th cucumbers more moisture, perhaps buy putting some kind of polythene just around the cucumbers.