I believe I was lied to several years ago when I was trying to buy a left over 04 GTO in October of 2004. I was eligible for GM Supplier, but the dealer said that you get the Supplier discount and that's it. You don't qualify for any rebates or anything - you either pay GMS or you get the best price plus incentives.
What's the truth?
GM always reserves the right to change the programs at any time, however, in my experience with buying with employee discounts, you get ALL incentives/customer rebates in place at the time of purchase contract finalization. PLUS, you pay the GMS or Supplier price, whichever program you qualify for. Best of both worlds. Based on your info, it sounds like the dealer was jerking you around, IMO.
ALWAYS call the GM customer service center or the GM Family First phone numbers and talk to them to find out your exact options to double check to see if what the dealer is telling you is correct. If you know what you can do going in, the dealer can't muck with you too much about it.
When I was looking for a truck, I went to a Chevy dealer first, asked if they took the employee discount, but wouldn't give me the price (I had already checked via GM Family First website so I already knew what it SHOULD be). He said it varies (????). I told him that it shouldn't. So...after trying to explain the GM employee discount program to the salesman and getting deer in the headlight look, I went down the road and bought a GMC without any hassles or BS, just the straight GM employee discount price.
About the Camaro...my feeling is they're going to want to sell them, and they'll offer Supplier and Employee discounts. There probably will be dealers that don't want to play...no problem. Go find one that does. DON'T be the first one in line because you may be subjected to big greedy dealer markups until supply starts to saturate the market. Wait a bit, the marked up prices will drop as the inventory increases.