Unity script to output to native UWP logs which can then be access via the device portal. Piggy backs on the Microsoft-Windows-Diagnostics-LoggingChannel provider as per this blog post https://blogs.windows.com/buildingapps/2016/06/10/using-device-portal-to-view-debug-logs-for-uwp/

UWPLogs.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
#if NETFX_CORE
using Windows.Foundation.Diagnostics;
#endif

public class UWPLogs : MonoBehaviour {

#if NETFX_CORE
    LoggingChannel loggingChannel;

    private void Awake()
    {
        Application.logMessageReceived += HandleLog;
        loggingChannel = new LoggingChannel(Application.productName, null, new Guid("4bd2826e-54a1-4ba9-bf63-92b73ea1ac4a"));
        loggingChannel.LogMessage("UWP Logging Started");
    }

    private void HandleLog(string logOutput, string stackTrace, LogType type)
    {
        loggingChannel.LogMessage(type.ToString() + ": " + logOutput);
    }
#endif

}