There is really no one answer to this question, and for some brokers, there is no answer.
Does the proprietary broker offer API trading, or some other form of connecting to their trade system to allow you to implement an automated trading system?
We have dozens of groups and more individual traders who use all phases of automation...from order entry through black boxes with FIX protocol. 10 or more to 1 non license, much more if Series 7.