Are flame holders made of a special material other than that used in combustion chamber?
In The Jet Engine, there is no mention of a two-material setup for the flame-holder/combustor. It's all about the design of the diffuser and combustor shape / holes.

One of the fancy things they mention (p. 122, image below) is the lining of the walls in elevated ceramic-coated tiles for internal cooling.



Having to deal with two materials would decrease the structural integrity of the combuster. And to my knowledge, the flame-holder and combustor are one and the same, a single unit.