Is it feasable to run some heavy computation (like DNN models) on PC and only stream ROS commands to the device? If this is supported, what is typical latency? Does this latency allow to steer Erle Copter or is just enough for Erle Rover?
Yes, check the documentation for that: http://docs.erlerobotics.com/robot_operating_system/ros/basic_concepts/configure%20your_network
With this method you can send directly the ROS commands using your computer.