I can't confirm if it works on Stock with a third party launcher, but I can't see any reason why it shouldn't,, perhaps someone on a stock based rom could confirm.
It's nice to finally have the widget available, so thought I'd pass on the tip!
Apologies if this has already been posted.. The latest version of Walkman (8.4.A.1.4) appears to finally allow use of the Walkman Widget in third party launchers, and on custom ROMS, something previously unavailable, which was incredibly annoying if, like me, you use Nova or Apex. Adding some widgets to my launcher, I spotted the Walkman widget in the list and it works perfectly. I'm currently running CM11 with Nova and finally have access to widget, so if you've been missing it, or trying to use third party widgets, it's now available regardless of which launcher you use.