1. It is not illegal for a company to have its own “Do Not Cold Call” list. If you know that poaching your allies’ employees is likely to jeopardize the joint projects, you may choose not to poach your allies’ employees. If you know that poaching your competitor’s employees will likely provoke them to poach your own employees, you may both choose to avoid the mutually assured destruction. As far as I know, it is only illegal to collude with your competitor to make such a list. But it appears that Google did have illegal agreements.
2. One of the quotes from a Google memo, “Most companies have non-solicit agreements which would limit or prohibit a candidate from asking a coworker to interview with us as well,” appears to have nothing to do with anticompetitive behavior. Instead, it probably refers to non-solicit agreements that employees often must agree to when joining a company that prohibit the employee from poaching one of their coworkers for a time after leaving the company. The memo warns not to pressure employees to violate contracts they have signed with their prior employers.