Not really, it just gives the Oneworld alliance more coverage when selling round-the-world/explorer fares tickets. They're happy for airlines outside of Oneworld to take part as it gives them destinations they might not serve themselves, and therefore makes their "explorer" packages more attractive.

Just look at the list of other carriers that are part of it. Aer Lingus (formerly Oneworld, now totally out of all alliances), Gulf Air (never show much interest in alliances) and Alaska (plays with members of all 3 alliances without much favour) all take part. Being part of the explorer tickets doesn't signify much, really.