Spacers are safe to use if installed properly and the correct length lug bolts are used.
I've used 10, 12, and 15 mm Turner and MS spacers. Not a single vibration with any of the Turner spacers yet when I switch to MS spacers on the same wheels I had significant steering wheel vibrations - Turner spacers
For a winter setup, I don't see any issue with running four 219M 18x8.5"et29 wheels. I'd definitely run the correct spacer thickness, even if it's > 12 mm, on the rear 8.5et29 to match the frontspacing of the 219M 18x9.5et23 rear wheel.