I found a great deal on nickel plated tri-y headers, however a member of my club warned me against them stating they get extremely hot because of the nickel plating. I've never heard that. Anyone else heard that?  

Ceramic coated headers will run cooler  

Yep, ceramic is better but the headers are only as hot as the gas that goes thru them minus the differental temperature change based on convective cooling. Nickel plated pipes I believe also have a tendancy to blue.  

jlg2002 said "I believe also have a tendancy to blue."

Yes they will blue or turn black. I found this out the hard way and ended up takeing them off and painting with VHT black. Finally gave up and put on 65/66 cast Hipo manifolds.

If they are a heck of a deal and you don't care about then staying shiney then go for it - but they will turn color on you.  

Ceramics are the best way to go.