When Hilton was in its heyday with concerts (70s-80s) it did not have a management company, it was managed by the University with a very aggressive asst manager who worked with promotors to get shows. He later went on to be the top guy at the Arena at Nevada Reno, worked for Bill Graham Presents (long time top promotor in San francisco, passed in 1991) and consulted on the San Jose arena construction during the 90's. He never worked for a management company, although he did work for Bill Graham as a tour director.
More recently, Jeff Chelesvig does not work for a management company at the Civic Center, who also worked at the ISU Center in that time frame. While there is evidence that management companies can help, they do take a lot of$$ out of the facility, more than the value of their "contacts" imo, Agents often appreciate independents and look for venues to keep competition going. Contacts can be nurtured without management companies via promotors and agents; local media and other marketing tools are more valuable than a management company, unless somehow a company has monopolized the market. Yes it takes entreprenurial skills to succeed outside a management company and you can't just be a calendar keeper (as you can for a management company)