Sort posts in loop by the WooCommerce Membership of the author

I would flag post as member_post when it is submitted to database and use this flag to sort them.

function wpse_287048_flag_member_post( $post_id ) {

    if ( wc_memberships_get_user_active_memberships() !== false ) { // Check if user is member
        update_post_meta( $post_id, 'member_post', 1 );
    } else {
        update_post_meta( $post_id, 'member_post', 0 );
    }
}

add_action( 'save_post', 'wpse_287048_flag_member_post' );

Then you are free to retrive your post sorted by member_post.

function wpse_287048_get_posts() {

    $query = new WP_Query(array(
        'post_type' => 'post',
        'meta_key' => 'member_post',
        'orderby' => 'meta_value_num post_date',
    ));

    return $query->get_posts();
}

Keep in my mind that all posts which you want to retrive must have member_post meta_key with some value otherwise they would not be selected from database.