Personally, I find that figuring out just what happens when Monster X meets Monster Y is half the fun of D&D. My Night Hag Family Tree is testament to this. And yes, it’s a game, so I don’t let genetics or DNA stand in the way of a half-dragon (deep) / half-hag (night), a half-dragon aasimar, or a half-kraken/half-human.
The image below is from revision 13 of my Night Hag Family Tree. I am working on revision 15, even now.
(edited to attach correct image)