I'm assuming by "G2 converter to Iray" you mean Iray Smart Converter? If so, it is possible, with some caveats. Smart Converter will apply to the whole figure, so you it first. Then use the manual method for NGS on any parts you want NGS on. For example, eyes. I like how NGS does eyes.
You can use the adjustments that ISC has on a figure you used NGS on, if I remember right, like brightness and gloss. But otherwise, running NGS or ISC will overwrite the other.
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