Just to give a difference of opinion, I don't think that this is necessarily representative of the entire HN community. I for one maintain a FB account almost exclusively for apps like this, so that I can reuse my social graph.
Disclaimer: I've done work in the past with one of the founders on a former iteration of this product.
Yours is not a bad idea, having a separate account, but I think that the number of people that have one is definately a minority respect the people that will just ditch the app because of it, worse, on mobile they will leave a bad review.
Disclaimer: I've done work in the past with one of the founders on a former iteration of this product.