Data point on the printed GC certs:

Bought $100 Hyatt gift cert from Raise.com on 11/9/17 for $80
Checked in the HR OC the same afternoon - FD agent told they won't accept the $100 cert at checkout
FD added that you need a PIN as the GC or cert must be purchased at Hyatt or Hyatt.com
Called Raise.com who told me that they never heard of this policy
Checked out on 11/11/17 and presented the $100 cert again. Not only it was accepted but the $100 value was there.

So, YMMV - is it worth taking a risk on a huge amount? No! But I'd buy from reputable outlet in small amounts with 20% or more savings and use immediately.