On April 4, 2018, the Alaska Supreme Court issued an order in State v Alaska Democratic Party, S-16875, letting the Democratic Party nominate persons who are registered independents. On August 24, the court issued a 24-page opinion, giving its rationale.
The key is that the Alaska Democratic Party had amended its bylaws last year to let registered independents run in its primary. The decision says that a party’s bylaws override state election law on this point. The decision is unanimous. Back on April 4, 2018, one justice had written that he hadn’t yet made up his mind, but now it appears he agrees with the majority. Thanks to Rick Hasen for the link.
Other courts that have ruled that parties may nominate a non-member if they wish include a U.S. District Court in New Mexico, and a state court in Colorado. The Alaska Supreme Court decision does not mention either of those precedents.