Nothing has been said about House of the Living Dead, but the distinct lack of any sketchbook or author's notes makes it certain to me that it will be recollected. It may be collected in one of the regular Hellboy trades, but I'm sure it'll turn up in a Library Edition one day. But it may be a while. There is another OGN being written at the moment, The Midnight Circus, and Mike Mignola wants to do more. You'll probably find once three of them have been released they'll get collected into a trade and that trade will eventually go to a Library Edition. It's for this reason that I have never bought House of the Living Dead.
Masks and Monsters won't be collected in a library edition, much the same as the two Weird Tales trades won't. They aren't really a part of the series.