Dread Cryomancer (Energy Substitution Undead)

[Warchon]

I'd like to explore the idea of applying the Energy Substitution feat to [Evil] spells in a 3.5 game, using the logic that [Evil] is a (Negative) Energy descriptor.
The specific application that I think makes this interesting is of course the Animate Dead and Create Undead lines, resulting in acid zombies, electric boos, and icebone skeletons. I feel like this would make a very thematic experience, but one possible immediate pitfall is that you are creating creatures with all the advantages of the Undead type but requiring a very specialized cleric to counter, since you would expect to need Elemental Turning/Rebuking, rather than the standard type. Also a concern is that I don't believe Electricity and Acid have opposites.
Another possible abuse lies with powered undead such as the Necrosis Carnex, which has a negative energy touch attack.
If [Evil] is implicitly negative, then [Good] is also valid here, and bottomless healing for the whole party is likely a headache for the DM.

What input or experience do others here have? Am I overstating the balance concerns? Are there other facets I may be failing to consider?

[Aniikinis]

You're forgetting something about the way the spells and the energy work. It's not the negative energy that makes them evil/good, it's the setting it's in. For example, if you were running a game in Amonkhet the create greater undead spell wouldn't necessarily have the [Evil] descriptor, it might have the [lawful] descriptor or no descriptor at all and the mummies created aren't inherently evil while within the walls of the city (naturally created by the wastes is a different matter). Negative and positive energy aren't moralistic in any way, they're amoral energies that power creatures/objects/whatever. They're no more good or evil than fire or air or any other "elemental" energy used in d&d.

For a good example of this fact, look at Heal and Harm. They directly use positive and negative energy respectively and do not have any alignment tags on them.

EDIT: Now, since this is the homebrew forum, you might want to think about an Alignment Substitution feat that acts similar to the energy sub feat, tweaking things to fit with it like Good-aligned undead or Evil-Aligned Lantern Archons.