No.
Sandman lately explained as much - in the official Japanese it becomes clear that Imu is a male:
For those that can't open it: "In Japanese chapters, male Celestial Dragon is called -聖, while female Celestial Dragon is called -宮. And Imu is called Imu-聖, so Imu is confirmed as male. "
Imu is the endboss of the entire series and from the brief confrontation with Sabo it becomes clear that he is VERY powerful.