As far as we know, all the Sekireis (with the possible exceptions of Kazehana, Hikari, and Hibiki) are. Not for lack of interest...Miya was deeply in love with Takehito, but they didn't have a lot of time together before he died. Remember that Takehito was obsessed with his work, and Miya was busy leading the Disciplinary Squad fighting off multiple invasions.
Keep in mind this might not be true. I recall one of the flashbacks with Takihito saying he'd love to have Miya experience motherhood. So, from a research of Sekirei standpoint I'm sure this would have been high on his "to do" list.
Not to mention, is a marriage really a marriage if no sex was ever involved? I mean other than a marriage for show...? (Ie Gengo and Erika in Freezing)