I think you need to do a little research on this. Not only did Red didn't have to worry about a salary cap, there was no free agency. Due to the option or reserve clause in all of their standard contracts, NBA teams basically owned a players' rights for as long as they wanted.
Read this:
Oscar Robertson Rule and note where it says, "the Oscar Robertson Rule, eliminated the "option" or "reserve" clause in the NBA's uniform player contract (which bound a player to one team for life at the team's option), and was the first step toward unrestricted free agency in the NBA".
Red could build a team and hold those players as long as he wanted and they had to take whatever contract he offered. As author David Halberstam once noted, "Red Auerbach went after the players of the highest intelligence and character, and then of course paid them horribly. They had great coherence as a team, great personal loyalty to each other, great respect and love for Auerbach, who had created this unique institution and honored each of them by making him a part of it, and then of course great anger at him for paying them so little.”