Slonimer,
By the terms of objective halacha you certainly can (except in situations where it would be Yichud for a date too. E.g. on a dark side road in the mountains). However, if the tznius standards of your particular community are against the practice, then you should not be poretz geder.
Eishes Ish and Nidda are both issurei erva with a chiyuv kares. Assuming the Yichud is d’oraisa, they are both Y’horag v’al Yavor. The only difference is that Eishes Ish, with eidim and hasra, gets misas beis din and Nidda does not. But that difference does not effect the issur Yichud.