I'm of two minds about this idea. On the one hand, it makes a certain amount of sense that the Beast Within would leave a certain...taint on the descendants of its hosts. On the other hand, this taint really, truly, deeply cannot be more Beasts; Harrowed are extremely rare beings and their numbers in the cosmos are rather fixed. How do you intend on pulling this off?
It seems to me it could just represent people who have a Beast in them but are do not actually take levels in harrowed. The potential is there, they just never bring it out in full. That is as opposed to it being their descendent. Then again, I could see it being done the other way, since as you mentioned the Beast could leave a taint on their descendants.