Offset aside, and assuming you use hubcentric AND wheelcentric spacers, if you have proper thread engagement, there is absolutely nothing wrong with running spacers.
Minimum 10mm thread engagement (on Subaru M12x1.25) #@ Torque Spec (56-75ft/lbs)
Missing any of those and your system is unsafe. If you have all 3, there is nothing unsafe about your system.
Somebody PROVE me otherwise with HARD DATA and I have $20 PayPal waiting for you.