“What are some of the ways to get employees involved in generating content (or content ideas) for a digital signage network?”
There are a couple of ways that I can think of to get employees involved in sharing or providing content, one would be to provide incentives for the employees that do provide content. Another would be to allow employees to participate in deciding on the type of content that is displayed. It really depends on the purpose of the screen though. If the screen is designed to gain employee participation, it could be easier to initiate a request to collect content, versus a screen that reports or informs generally from a specific group within the company.