Rather than turning nginx into a service,  or using CMD to start a process, which really doesn't seem to work.  I found that Powershell makes it easy to startup nginx as a detached process. I've combined starting nginx with PHP. Below is the script, named "start-nginx.ps1"
$fcgiPort = "127.0.0.1:9000"
$PHPini = "c:\php\php.ini"
$ErrorActionPreference = "SilentlyContinue"
function restart { 
Push-Location /nginx
Stop-Process -Force -Name nginx 
Start-Process ./nginx.exe   -WindowStyle Hidden 
Stop-Process -Force -Name php-cgi
Start-Process  "c:\php\php-cgi.exe" -ArgumentList ("-b" + $fcgiPort  +  " -c "  +  $PHPini)   -WindowStyle Hidden 
Pop-Location
}
restart
This script can be executed from any directory, but needs to be customized for where your nginx installation is located.  
This script includes a silent attempt to kill nginx and PHP before launching both. 
Windows systems are supposed to recognize ".ps1" files as powershell, even in the CMD prompt.  
I created another small script to kill the running processes,  which simply removes the "start-process" lines from this file. 
To run at startup, I used the win-R command to navigate to the directory shell:startup
Placing a shortcut to the startup script in this directory,  nginx starts at boot!
Powershell also includes a much more sophisticated ability to schedule tasks, and it is possible to schedule this script to run at startup. See This Link
From the article:
 >powershell
 $trigger = New-JobTrigger -AtStartup -RandomDelay 00:00:30
 Register-ScheduledJob -Trigger $trigger -FilePath $HOME/start-nginx.ps1 -Name startNginx
Combined, I think this approach gets you everything you'd need from an nginx windows service and doesn't require any third-party applications.