Battery power supply for Arduino and DC motors with L293D
Yes, you can have multiple devices hanging off the same pair of supply rails.

You should not have multiple ground paths though - like the ground-to-ground connection shown between the Arduino and the L293D in the diagram. Ideally, all the devices should connect to each other and the supply ground at a single point, to avoid ground loops.

Also add hefty capacitors (10 to 100 uF) between Vcc and Gnd pins of each device to decouple the supply.