Q. Can fat-free evaporated milk be substituted for heavy cream?
These questions always, always depend on the context. You can whip evaporated whole milk and use it as something of a substitute for whipped cream (it needs to be partially frozen first). The same is not true of low-fat or fat-free evaporated milk.
The more telling question, though, is, why is heavy cream specified in your recipe? If the recipe writer didn't want 36% butterfat (either for taste and richness, or to help keep the mixture from curdling), she would have specified milk or skim milk or water. Fat-free evaporated milk has none of the fat, none of the richness of cream, or even the 7.9% fat found in evaporated whole-milk. It simply has a higher percentage of dissolved milk solids and proteins than plain skim milk.
Might fat-free evaporated milk work in your recipe? Perhaps, and if you're used to consuming fat-free dairy products, it is possible that you might prefer the final product to one swimming in fat. But it is also possible that the dish will flop, either because it is too runny, too bland, or has curdled.