Question: From <http://en.wikipedia.org/wiki/Mutant_%28fictional%29#DC_Comics> 

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> Mutants play a smaller, but still substantial role in DC Comics
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However, that particular Wiki article only mentions very few mutants (Captain Comet, and a couple of Batman adversaries), neither of whom strike me as important enough to warrant "**substantial**" role.

Was that expression inaccurate? Or are there really mutants who play genuinely substantial role in DC universe?

Answer: 
The issue at hand is the DC Universe's definition of mutant. Finishing off your quote:

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> DC Comics **does not make a semantic or an abstract distinction between humans (or superheroes/villains) born with mutations making them different from humans mutated by outside sources**.
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This is to say by DC standards, Spider-man is a mutant, not a mutate. This opens up our definition and the number of applicable characters.

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> Also characters who were transformed through radiation or a mutagenic gas are sometimes identified as mutants instead of Marvel's term, 'mutates'.
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> All humans with powers are simply referred to, and treated as, one group collectively known as *metahumans*. The term mutant does still exist for humans born with actual powers instead of attaining them.
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Here is a handy picture for DC supers:

![enter image description here](https://i.stack.imgur.com/BRAAq.jpg)

And for Marvel:

![enter image description here](https://i.stack.imgur.com/jMTta.jpg)

So anyone who's been 'mutated' by an external force would be considered a mutant in their lexicon. For instance, *The Flash* might be considered a mutant, as the chemicals he was exposed to mutated him. Because of the huge overlap with metahumans though, and being the more general case, they're often just called meta humans.
DC steers away from the Marvel version of *mutant*, perhaps because it plays such a major role at the *House of Ideas* or simply because they feel no need. There are mutants within the DC Universe and have been for some time; the first I can recall is ***Captain Comet*** who, if memory serves, left the Earth *because* he was a mutant and different from other humans.

Others include **Jade** and **Obsidian**, the children of the Golden Age **Green Lantern** and **Nuklon** or **Atom Smasher** as he is now called - all of whom were founding members of **Infinity Inc.**, the legacy group of the **JSA**.

*Metahumans* seems to be the operative word of choice at DC and encompasses (pretty much) all heroes and villains with powers.