Yep they use it for their handoff stuff.
I’m reading reports in some forums I trust of 2009 machines with upgraded 2010 firmware are installing High Sierra without issue. Seems you have to have a MAC video card to do the install but after the initial install a 3rd party nVida card will work just fine.
Since I never install a new OS for at least a year after it’s release I’ll be fine. When Apple does cut me off from OS upgrades I will just use Windows 10 in place of macOS. The machine works just fine for my needs in pro audio either way. I just prefer OS X or macOS.