Tire manufacturers show specs for each of their tire models and sizes, including an approved range of rim widths. The tire can be mounted on wheels with widths anywhere in that range, without safety issues. Tires tend to look a bit stretched at the upper end of the range, and a bit bulging at the lower end, but anywhere in between they should look fine.
Most 255/35-18 tires are approved for mounting on widths of 8.5-10.0". So they can be mounted on 18x10, but yes they may look a bit stretched. 265/35-18 are usually approved for widths of 9.0-10.5", so they may look less stretched on an 18x10 than the 255/35-18. And if you go for the unnecessarily oversized bling-bling 275/35-18, those are usually approved for widths of 9.0-11.0".
I agree with the comment above that you would be better off with 19" rears if you insist on 18" fronts. Due to the difference in outer diameter, the NSX tends to look a bit unbalanced with same-diameter wheels front and rear. But you would be even better off with 17" fronts and 18" rears, as there are a lot more choices of top-performing tires available in the NSX sizes for wheels of those diameter.